Hitting speed bumps on the hydrogen highway.

I push the pedal to the metal as I challenge another journalist driving down Folsom Street in San Francisco to see who can make it back to the Sierra Club convention first. She's driving an SUV, a 2006 Mercury Mariner with a gasoline/electric hybrid engine. I'm in Ford Focus with a hydrogen fuel cell. There's no provocative "vroom, vroom" when I jam the accelerator at a standstill. I have to lower the windows to issue my dare.

I win.

"Awesome driving," says Sierra Club spokesman Eric Antebi from the backseat, as I pull into the staging area. He's already tickled at the odd convergence of Ford, Honda and Toyota at the Sierra Club's eco-convention. So he's happy to humor a Republican global-warming agnostic with a lead foot.

Detroit has joined Japan in recognizing a market for more fuel-efficient cars, as all automakers are looking now at putting hybrid engines in bigger cars.

Later, I drive the Mariner and find that what the folks at Ford say is true: The hybrid Mariner may cradle a four-cylinder engine, but, as the show-floor crew intoned, "with the performance of a six-cylinder." The Mariner hybrid boasts 33 miles per gallon in the city/29 mpg on the highway -, a big boost from 22 city/26 highway stats for the all-gas version.

Finally, Ford and its divisions are looking to improve fuel economy.

Except now--talk about bad timing--the Bush administration is poised to poison the well. It has proposed questionable changes in federal fuel-efficiency standards for SUVs and light trucks.

I should note, the Bushies have not proposed changes in corporate average fuel economy standards--known as Cafe--for sedans, which would remain at 27.5 mpg. Also, Bush already has raised standards for SUVs, light trucks and minivans--the 2005 standard is 21.2 mpg for light trucks; it will rise to 22.2 mpg in 2007.

Now, alas, the Bush administration is pushing for what it calls tougher standards for trucks and SUVs, with different standards based on size. The bigger the vehicle, the more gas the Busbies will allow it to guzzle. Under this plan, the fuel-economy standard for the smallest SUV models would be 28.4 mpg by 2011, while the Cafe standard for the largest vehicles--like a Dodge Ram truck--would be 21.3 mpg in 2011. For now, Team Bush would exempt Hummers and other monster trucks that weigh more than 8,500 pounds, because they are so big they are considered commercial vehicles.

The environmentalists are suspicious--and rightly so, because the new rules would enable the Big Three to get around the new Bush standards simply by making bigger cars. Thus Dan Becker, the Sierra Club's global-warming czar, dismissed the new Bush plan as "allowing the auto companies to decide whether we save gas or not."

Dianne Feinstein, D-Calif., was one of five U.S. senators who responded by asking Bush to end the "SUV loophole" and make all vehicles meet the 27.5 mpg fleet average--rather than create a more elaborate SUV loophole. While Detroit complains about niggling federal regulations, closing the loophole would allow car manufacturers to decide how best to meet a universal standard. Selling more hybrid models might well be the ticket. The technology exists. The cost is reasonable and getting better.

One problem, one of the car guys tells me: The public has to want fuel-efficient cars.

We are standing on Howard Street, watching SUVs dominate the streets of San Francisco. If consumers in this haven of the left choose to buy gas-guzzlers and refuse to exercise personal responsibility when they shop for wheels, they have little business blaming Bush for not being strong enough on the environment.

Bush should end the SUV loophole, if only to increase America's energy independence and air quality.

And Dubya should end the pricey program that he claims will innovate America out of a future energy pickle. Specifically, in the wake of Hurricane Katrina, with federal spending about to go boom, Bush should pull the plug on his Freedom Car--with the "Car" standing for Cooperative Automotive Research--program, which is supposed to develop hydrogen fuel-cell cars after the taxpayers plunk down up to $2 billion on research.

I drove a hydrogen car Friday and had a fun ride. But with a price tag of $1 million to $2 million per fuel-cell car, it's pie-in-the-sky stuff'. A Ford executive admitted it would be "a decade or two" before hydrogen fuel-cell cars are commercially viable.

Sorry, but one or two decades is what they always say. Why not? In a decade, there will be another president who can propose a different program.

Meanwhile, taxpayers shouldn't have to foot the bill for fuel savings that may or may not happen ever. As the Sierra Club's Antebi noted, hybrid "technology is on the shelf and it can be applied to almost any car." Now.

As gasoline pushes $3 per gallon, Bush would be doing Detroit a favor. He'd even be helping out gas-guzzlers. Then again, these days they need a break.

Debra J. Saunders writes a column for the San Francisco Chronicle.