After a summer of political quiet on the issue, U.S. automakers, environmentalists and motorists are preparing for another Capitol Hill collision over proposed fuel economy standards that could lift the average car's gas mileage to 35 miles per gallon by the year 2020.

The first end-of-summer salvo came from the SUV Owners of America, a nonprofit lobbying group that says it represents the interests of light truck, minivan and sport utility vehicle drivers.

The group paid for ads in the Post-Gazette, the Arizona Republic, the South Florida Sun-Sentinel, The Star-Ledger of New Jersey and other newspapers. The full-page color ad warned that certain members of Congress would effectively "outlaw" bigger SUVs if they enacted the Senate-endorsed Corporate Average Fuel Economy revision, threatening the very lifestyles of motorists who like using bigger, safer vehicles to tote their kids and tow their boats and RVs.

"As we went to save gas, we lost safety," said Barry McCahill, the president of SUVOA, whose board members consist of leaders from trade groups representing RV and marine retailers.

In June, the Senate approved an energy bill that, for the first time in two decades, would require major improvements in gas mileage. In August, House Democratic leaders bypassed the chance to discuss their own proposed CAFE standards during an open debate on energy legislation, hoping that a few more months of private discussion might allow Democrats to avoid a public, intra-party fight over how far to push the Detroit automakers and their unions.

But the issue likely will come up this autumn.

The auto industry, meanwhile, is pushing for a bill that imposes less ambitious mileage improvements. The Hill-Terry Bill targets an average fuel economy of 32 to 35 miles per gallon by 2022.

That bill, supporters say, creates separate standards for cars and trucks and foreign and domestic fleets, giving automakers needed flexibility. But environmental groups say the bill would save only one-third the gasoline that the stricter standard would.

If automakers are forced to improve average gas mileage across their respective fleets, something's got to give. Either towing capacity goes down, or the price goes sky-high, or the vehicle becomes lighter -- meaning less safe, Mr. McCahill said.

Of course, the automakers may simply scrap certain low-mileage models -- although those also carry the highest profit margins.

Or, the opposite may happen -- in order to improve a company's average fuel mileage equation, the company may not rid itself of Tahoes, Suburbans and Escalades, but instead may overproduce high-mileage models, more than the buying public wants.

Ford Motor Co. President and Chief Executive Officer Alan Mulally said as much last month during an industry panel discussion. "You're trying to force-feed the market rather than being market-driven," he said, according to the Associated Press. "I've never seen a market-distorting policy like CAFE."

But new numbers reported by the National Highway Traffic Safety Administration suggest, at least to proponents of stricter CAFE standards, that the American appetite for higher-mileage vehicles is exceeding the industry's willingness to provide such options. During the 2007 model year, the average mileage for all new autos sold will be 26.4 miles per gallon, nearly a 4 percent increase in mileage over 2006.

"Hybrid sales are booming," said David Friedman, vehicle expert at the Union of Concerned Scientists, a group that has battled industry and the Bush administration on policies they believe to be detrimental to the environment.

"Ford has limited production of Escape hybrids [while] Toyota Prius is among the top-selling cars in the country," he said. "People are very interested in [hybrids]."

"It makes no sense at all for Congress to push extreme measures on fuel economy that would devastate the domestic auto industry," United Auto Workers President Ron Gettelfinger told the Detroit Economic Club last week. "Make no mistake: If the fuel economy measure that passed the U.S. Senate becomes law, it will have a major negative impact on the auto industry."

A spokeswoman for U.S. Rep. Jason Altmire, D-McCandless, said the most likely scenario was that the House first will vote on a compromise bill that emerges from House-Senate conference committee meetings. That bill, she said, probably will look a lot like the original CAFE revisions approved by the Senate.

The SUVOA, in its ad campaign, urged readers to contact Mr. Altmire's office and other lawmakers to protest the stricter CAFE standards. However, spokeswoman Christina Stacey said the congressman's offices had received 200 phone calls in favor of higher fuel economy standards.