SAN FRANCISCO -- Will Matt Gonzalez soon become the Green Party's first mayor of a major U.S. city? Gonzalez faces centrist Democrat Gavin Newsom in a Dec. 9 runoff election in San Francisco. And while the smart money is on Newsom, who ran well ahead of Gonzalez in a crowded Nov. 4 general election, there is reason to believe that a tight race is possible. The election may come down to whether San Francisco's large constituency of progressive Democrats can bring themselves to back a Green for local office.

Gonzalez, who is currently president of the San Francisco Board of Supervisors, won 40,714 votes in November, compared with the 87,196 votes claimed by Newsom, who is also a supervisor. But candidates who ran to Newsom's left grabbed an additional 72,539 votes -- and of those, 54,898 went to two candidates who share Gonzalez's progressive populism. (This is San Francisco, after all, so the lone conservative combined with a trio of fringe candidates to total fewer than 8,000 votes.) These numbers are encouraging to Gonzalez and his supporters, but the candidate's Green Party membership has added a partisan twist to what might have been a straightforward showdown between San Francisco's progressive movement and its deal-making, power-brokering Democratic establishment. The problem for Gonzalez is that in an overwhelmingly Democratic city, partisan politics typically benefit, well, Democrats. For evidence, consider the recent gubernatorial recall election: Democrat Cruz Bustamante, who ran an inept campaign, won 63 percent of San Francisco's vote; Arnold Schwarzenegger, who won the statewide tally handily, claimed just 19 percent.

Consider also that in the 2002 governor's race, Green Party candidate Peter Camejo picked up 33,495 votes in San Francisco, and in 2000, Green U.S. Senate candidate Madea Benjamin grabbed 32,377 votes in the city. In other words, the Green base probably provided the vast majority of Gonzalez's roughly 40,000 votes in November. All of which means that to compete in December, he'll have to pick up support from thousands of voters who have never voted Green before. Early polls provide little help in trying to sort things out. One showed Gonzalez holding a narrow lead, but another put Newsom 14 points ahead (with 16 percent of voters saying they were undecided).

So liberal and progressive Democrats hold the key to what could be a competitive race. Gonzalez needs to get people who supported other left-leaning candidates in November to the polls -- and to capture an overwhelming majority of their votes. Newsom recognizes this, and both candidates are working overtime to corral support from unions, gay and lesbian organizations, liberal elected officials and progressive voters. They've each had some success. Newsom has signed up more unions (including building trades, uniformed services and utility workers locals), but Gonzalez won the backing of two Service Employees International Union locals, as well as the hotel and restaurant union, and the supermarket workers. Each candidate has also won the support of one of San Francisco's two big gay and lesbian Democratic clubs, and backing from different supervisors. The third- and fourth-place finishers in the general election -- Angela Alioto and Tom Ammiano -- remain uncommitted.

Newsom seems to realize that the election will hinge on progressive voters, and he's pitching his liberal credentials whenever given the opportunity. Speaking before a national gathering of moderate Democrats in San Francisco recently, for example, Newsom declared his strong support for gay and lesbian rights. "You might not support me after hearing this, but I'm pro-gay marriage," he said. Later that day, on a walk through Chinatown, he pointed to diversity as the city's greatest strength, made a pitch for investment in senior centers and child care, and extended his earlier endorsement of gay and lesbian rights to include transgendered individuals.

He is also playing the Democratic card for all it's worth, lining up endorsements from current Mayor Willie Brown and most of San Francisco's representatives in Sacramento and Washington. Even Al Gore is expected to put in an appearance for Newsom. Notably absent from this list, however, is state Senate President John Burton, California's most influential liberal lawmaker and a power broker in San Francisco politics. The city's Democratic Party also endorsed Newsom, but roughly one-third of its central committee voted against that backing.

"I'm defending being a Democrat in this town," Newsom says as part of his standard speech to Democratic audiences. This approach has worked with some party members. "Progressivism is always with the Democratic Party," says Richard Ow, a member of the city's Democratic committee. "We cannot have a Green in City Hall. The Democratic base cannot be divided."

But it hasn't worked with others. The Rev. Norman Fong is a Presbyterian minister in Chinatown and a lifelong Democrat, but he was swayed to support Gonzalez when the candidates presented their platforms to a group of 1,000 mostly elderly and poor residents. "Newsom wavered on some real protection for tenants," Fong recalls. "We don't want wavering. There are people who want to tear down Chinatown. Tear down these old buildings and that's the end of affordable housing." Gonzalez and Newsom share similar positions on boilerplate civil-rights issues. But for Democrats like Fong, Gonzalez's stronger track record of advocating for social justice trumps Newsom's credentials as a member of the Democratic Party.

Municipal elections in California are supposed to be nonpartisan affairs. In major urban centers, in fact, runoffs frequently pit two Democrats against each other. In recent years, this has often led to a progressive running against a mainstream or business-oriented Democrat. Two years ago, the Los Angeles mayoral runoff -- which saw progressive Antonio Villaraigosa opposing the eventual winner, Jim Hahn -- drew national attention to this trend. A year prior to that in San Francisco, Ammiano's energetic attempt to unseat Brown created expectations that, come this year, the leading candidate to replace the term-limited Brown would come from the progressive camp.

This was never a sure thing, however, and some of the challenges Gonzalez faces have to do with weaknesses in the city's progressive movement. Most important among them is that labor is not organically linked to the city's liberal landscape, and some local populists -- Gonzalez among them -- don't quite understand the essential role unions can play in progressive municipal politics. I recently asked Gonzalez about the significance of labor to the broader progressive movement, prefacing my inquiry with an observation about the role unions play in Los Angeles, where they're the heart, soul and muscle of liberal politics. Gonzalez's answer was brief and technical, and he seemed disinterested in pursuing the point further. "Labor has been instrumental in winning elections, but has also supported losing candidates," he said. "You have to make a race-by-race assessment."

San Francisco's progressive movement is also too wrapped up with neighborhood-based anti-growth activists to forge a genuinely progressive position on development. To its credit, progressive San Francisco has defended working-class neighborhoods against gentrification and unaccountable development. But it's been less adept at supporting projects that would bring positive development -- more housing, especially affordable housing, and better jobs -- to neighborhoods. Despite Gonzalez's emergence, the electoral face of progressive San Francisco also continues to be disproportionately white, and coordination between different progressive camps is spotty. That four major candidates ran to Newsom's left in November points to this lack of cohesion.

Newsom's success, Ammiano's floundering (he finished fourth in the general election) and Gonzalez's emergence have changed the equation of city politics, throwing a partisan variable into the mix. Yet the underlying division remains one that is based more on ideology and vision than on party affiliation. In fact, the most acrimonious divisions in San Francisco politics have not been between Democrats and Greens or between Democrats and Republicans (a virtually inert group in the city) but between, on the one hand, progressive activists and their allies on the Board of Supervisors and, on the other, Mayor Brown and his supporters in the business world, black and Chinese American leaderships and among some segments of labor.

Both candidates in the race present themselves as the person best equipped to change San Francisco. Newsom says he will reverse trends that he claims have empowered the Board of Supervisors at the expense of the mayor and soured the city's business climate while lessening its quality of life. Gonzalez positions himself as the candidate who will empower low-income residents, artists and the disenfranchised, all while changing the way development and city planning take place. Both candidates are young -- still in their 30s -- but they represent different constituencies and different philosophies.

This first election of the post-Brown era was supposed to be a referendum on the direction of San Francisco. Would voters pick an insurgent progressive to lead the city, a representative of the neighborhoods, tenants and bohemian and working-class San Francisco, or would they choose a favorite of the downtown business community and affluent young singles and childless couples -- straight and gay -- who have turned the city into a post-adolescent playground? Would there be a political realignment in which Brown's more liberal backers -- notably labor unions and black voters -- moved into the progressive camp or would they remain linked to the city's establishment through the traditional Democratic leadership and old-boy networks established during Brown's long years of political leadership? (Before becoming mayor, Brown spent 15 years as the powerful speaker of California's state assembly.)

On some level, this is what the race is still about, and the most divisive issues have to do with social justice and the place of low- and moderate-income residents in San Francisco's future. Despite his liberal leanings on many social issues, Newsom's politics are intertwined with those of the city's business establishment and other conservative economic groups. This is Newsom's natural constituency. He lives in and represents one of the city's wealthier communities and has had close business relations with one of San Francisco's old-money clans, the oil-rich Gettys.

Unlike Gonzalez, a former public defender, Newsom has not been a leader on social-justice issues. In a city where low- and moderate-income renters are threatened by the nation's highest housing costs, for example, Newsom is critical of rent control and outspoken in his defense of property rights. He has also attacked Gonzalez's proposal to create land trusts as vehicles for affordable homeownership as too radical and too out of touch with San Francisco's mainstream. Both candidates say more affordable housing needs to be developed, particularly housing that would increase home ownership, but they differ on whom the target beneficiaries should be. Newsom wants to grant incentives to developers of projects downtown and along the waterfront who will reserve a "large percentage" of units for sale to households earning 120 percent or less of the city's median income. That's in line with the city's current inclusionary zoning rule, which mandates that 12 percent of the units in large residential projects be set aside for households earning up to 120 percent of the city's median income. In addition to his land-trust proposal and suggestions that rent control be strengthened, Gonzalez wants inclusionary zoning rules to require that 20 percent of the units in sizeable market-rate housing developments be affordable to people earning 50 percent of the median income. Each proposal has its merits, but what's clear is that Gonzalez is willing to demand more from developers on behalf of a population with lower incomes.

A look at the ballot initiatives the two leaders have supported further illuminates the differences between them. Newsom has ridden a pair of Rudolph Giuliani-esque proposals on homelessness to prominence. One would replace the relatively high cash payments certain homeless people receive with a package of services and much smaller cash disbursements. The second initiative would place tough restrictions on "aggressive panhandling." For his part, Gonzalez authored and campaigned for a ballot measure increasing the minimum wage in San Francisco. (Tellingly, he did so with little input from labor.)

Unfortunately for the political oddsmakers, all three initiatives passed easily, providing little guidance as to which candidate San Francisco might choose in December. This reveals a conflicted city -- a city that Newsom and Gonzalez together represent well. Newsom represents a middle-class burg that's concerned with quality-of-life issues and is committed to a very mainstream vision of stability in an urban setting. Gonzalez is more of a gambler. He appeals to San Francisco's liberal soul and its history of embracing the outsider. He wants to preserve a place in San Francisco for the poor and the working class, many of whom have already had to flee the city.

This election won't end the struggle over San Francisco's future, but it will probably decide the city's direction for at least the next few years. Liberal and progressive Democrats have an important role in determining the immediate fate of their local government. Newsom's camp hopes party loyalties will win out; Gonzalez hopes that liberals and progressives will vote for the candidate who comes closest to their political views. Taken together, Newsom and Gonzalez may represent the city well. But on Dec. 9, only one can become mayor.

James B. Goodno writes about politics and policy in the American West and Southeast Asia.