If you listen real hard, you can hear Harry and Louise revving up their SUV, preparing to drive right over any effort to “kill economic growth” or “raise costs on the consumer” with “job-killing” carbon taxes.

Green groups still have time to slit the SUV’s tires … but not much time.

Barack Obama is poised win the presidential election in less than three weeks, but environmental organizations don’t have time to celebrate the Democrat’s expected victory. Instead, several leading climate change activists say, enviros need to start organizing now to build a constituency that will support an Obama administration’s efforts to combat the biggest challenge of our time.

That’s the view offered Saturday morning by the likes of David Orr, head of the Presidential Climate Action Project, Bill McKibben of 350.org, and Gillian Caldwell of 1Sky.org. Their call to action was made at the Bioneers conference in San Rafael, Calif., a three-day, distributed festival of ideas and networking that’s been convening for 18 years.

Regular Grist readers are familiar with most of the facts thrown out by the enviros: Dramatic cuts in CO2 emissions are needed over the next decade to avert significant rises in global temperatures, agricultural and water systems around the world are imperiled, the rush to extract remaining oil reserves is destroying fragile ecosystems …

But it was the passionate call for political organization that caught this observer somewhat by surprise. If, as seems more and more likely, Obama is elected, any changes he hopes to make in U.S. energy and climate policy will be opposed by well-organized and funded industries. Big Oil’s clout in Washington, after all, is such that this year it was able to block an extension of the moratorium on offshore drilling.

All this brought to mind memories of 1992, when then-candidate Bill Clinton was campaigning hard on health-care reform. Say what you will about how the Clintons handled (or mishandled) health care, but the deep-pocketed health insurance industry, drugmakers, hospitals, and a huge coalition of big and small businesses organized a multi-front campaign to head off health-care reform. And it worked.

So what needs to happen to avoid having “Harry and Louise” hijack the national debate over the looming climate disaster?

For Caldwell’s group, it’s about organizing people in every voting precinct in the nation. 1Sky is looking for “precinct captains” who will evangelize at the local level, making sure voters are communicating with elected officials.

McKibben and 350.org, meanwhile, want Americans to pressure the new presidential administration to reengage in international climate talks. And they hope to encourage people around the world to engage in public action — rallies, protests, staged events, etc. — to push leaders of every nation to work on a successor to the Kyoto Protocol.

Orr’s group has developed a 100-day action plan for the next president, which can be found on the PCAP Web site, with a shorter, more accessible version to be released as an e-book later this fall. A big part of the argument is using economic stimulus to fund a green tech revolution that would produce millions of new jobs.

But is all this enough? Change is scary, and the companies with a vested interest in the carbon economy are adept at playing on Americans’ fears. It’s up to environmental groups to start organizing now. The next president will need all the help he can get.