HOUSTON – The nation's fourth-largest city, once dominated by Big Oil, is warming to greener options as it chooses a new mayor.

Voters in sprawling Houston, a city crisscrossed by clogged freeways and freewheeling development, are picking from a low-key field of mayoral candidates who are focused on public transit, regulated development and environmentally friendly policies.

The Nov. 3 election reflects "a major consensus that is surprising for Houston, a consensus for planning, a need for light rail, a need to move beyond oil and gas," said Stephen Klineberg, director of the Urban Research Center of Houston at Rice University. "It's reflecting a real evolution of a city reinventing itself for the 21st century."

No clear favorite has emerged in the race to succeed Bill White, who served three two-year stints that included his high-profile welcome of more than 150,000 evacuees from Hurricane Katrina-ravaged New Orleans in 2005. White, barred by law from another term, plans to run for the 2010 Democratic nomination for U.S. Senate if Kay Bailey Hutchison resigns to run for governor.

The mayoral candidates are former city attorney Gene Locke; city controller Annise Parker; urban planner Peter Brown, an architect and former city councilman; and retired Air Force officer Roy Morales, a county school trustee.

Early voting began Oct. 19. If no one wins a majority in November, the top two finishers will meet in a runoff, likely in December.

Locke, 61, would be Houston's second black mayor. Parker, 52, would be the city's first openly gay mayor and second woman in the job. Morales, 53, would be its first Hispanic mayor, but is considered a long shot. Brown, 72, who is white, has the most money to spend — much of it loaned from his wife, oil-field services heiress Anne Schlumberger.

Although the ballot is nonpartisan, Locke, Parker and Brown are Democrats. Morales has tried to distinguish himself as a conservative Republican. Houston, which President Barack Obama carried in 2008, is largely Democratic, although the surrounding suburbs are conservative.

Houston is about 25 percent black and one-third Hispanic. Its gay population is estimated at about 60,000.

The winner will lead almost 2 1/2 million residents — up nearly 14 percent from 2000, as Houston has weathered the recession better than many cities.

But Houston hasn't been totally immune to economic woes: Unemployment of 4.1 percent a year ago is almost twice that now. And declining sales and property tax revenues in a city with no income tax mean the new mayor could inherit what Parker has estimated to be a shortfall of more than $50 million in the $2 billion budget that took effect July 1.

It's been a polite campaign, partly because the four contenders have much in common.

"The major candidates do not disagree much on the major issues facing the city, nor have they gone after each other personally," said Richard Murray, a University of Houston political scientist.

Parker has said she'd help neighborhoods enforce their deed restrictions — Houston's version of zoning of property for particular uses. Locke advocates expansion of the 7.5-mile light rail system and "building green" through developer incentives for environmentally friendly construction.

Brown, who has made "smart growth" the centerpiece of his campaign more than his competitors, has said the city should emphasize creation of neighborhoods where people can live, work and shop. Morales favors government reduction and a property tax cut to stimulate the economy.

They've all talked about building on White's successes and guiding Houston out of the recession.

"I'm the only one in this race who's conducted tough audits, identifying millions of dollars in savings, money that's not working for you in parks, in libraries, in neighborhoods, in the police department," Parker said.

She is looking to follow Kathy Whitmire, who used the controller's job as a springboard to become Houston's first female mayor in 1982.

Locke, the former city attorney, has attracted endorsements and financial backing from business leaders, cashing in on his three-year tenure in the 1990s under popular mayor Bob Lanier, who supports him. Locke has cultivated city insiders since then as legal counsel to several government agencies.

"We get things done in Houston," he says in a TV commercial. Locke raised nearly $1 million over the summer and had more than $1 million for the final weeks, compared to Parker's $223,000.

Brown, the urban planner, has a whopping $2 million for the late push to Election Day. He touted his City Council record of supporting energy conservation and environmental issues. His plan, he said, would provide "a clear business strategy and a dedicated business-friendly approach to government."

Morales, by contrast, had roughly $4,600 on hand in his bid.

Klineberg said a signature issue like mass transit, once a campaign loser in Houston, represented a "paradigm shift."