WASHINGTON - Competing proposals to raise fuel economy standards for automakers have set off a fierce lobbying effort in Congress and across the nation by environmental activists, the auto industry, and union workers, according to the Associated Press.

"The future competitiveness of our company is at stake," wrote DaimlerChrysler AG's Chrysler Group President Tom LaSorda in a recent e-mail to more than 30,000 employees. "As soon as possible, let your voice be heard — loud and clear."

An automobile trade group was airing new radio and print ads in about 20 states and Washington to build support for an alternative proposal pushed by Sens. Carl Levin, D-Mich., and Kit Bond, R-Mo., that would seek more moderate increases to gas mileage rules.

Environmental groups, meanwhile, have been running their own advertising in key states to solidify support for a Senate energy package that would require each automaker's fleet of new vehicles to average 35 mpg for cars and trucks by 2020, an increase of about 10 mpg over current levels.

Interest groups are expected to descend on Capitol Hill to lobby for the fuel efficiency rules and mount letter-writing campaigns from afar. Dealers representing both domestic and foreign automakers plan to meet with lawmakers, while several environmental groups have mobilized support for the proposal backed by Sen. Dianne Feinstein, D-Calif.

"Our members are really up in arms and calling and writing and e-mailing and visiting their senators back home," said the Sierra Club's Dan Becker.

The Senate expects to consider proposals the last week in August to increase fuel efficiency requirements for new vehicles as part of its deliberations on an energy bill. The issue is critical to automakers because they develop their vehicles years in advance and any efficiency improvements would need to be included in future cars and trucks.

Proponents of the Feinstein bill, which would also seek a 4-percent annual increase in fuel efficiency rules from 2020 to 2030, say it would help address concerns about global warming and gasoline consumption. They also question whether the auto industry can be trusted to develop significant efficiency gains after battling past attempts to increase the standards.

"The technology exists today to make major improvements in fuel economy," Feinstein said Thursday. "It can be done without sacrificing safety, and with significant benefit to our economy and the environment."

The auto industry has opposed the bill, saying it would force them to comply by scaling back the number of large trucks and SUVs they offer. The new standards would cost them billions of dollars, threatening auto plants and workers' health care benefits, they contend.

"Hundreds of thousands of those jobs are at stake here," said former Sen. Jim Talent, R-Mo., who spoke on a conference call arranged by the Alliance of Automobile Manufacturers. The trade group is running print and radio ads to encourage support for the Levin-Bond plan.

Underscoring the concerns, LaSorda wrote in his e-mail to employees that the Feinstein approach would "add up to a staggering $6,700 — almost a 40-percent increase — to the cost of every Chrysler vehicle."

The alternative, supported by Democrats Mark Pryor of Arkansas and Debbie Stabenow of Michigan, would require passenger cars to meet a fleet-wide average of at least 36 mpg by 2022 and 30 mpg for pickup trucks, SUVs, and vans by 2025. It would seek to promote flexible-fuel vehicles and other alternatives.

The United Auto Workers asked members to contact their senators about the proposals. In an e-mail to workers, the union said the Feinstein approach would force the industry "to off-shore small-car production and drastically downsize their vehicle fleets, which would result in job losses at plants where pickup trucks and SUVs are assembled."