The Carter administration, over strong protests from the auto industry, yesterday refused to back down from the government's tough 1985 standards for fuel economy, warning that the added costs to the consumer were outweighed by the need to conserve energy.

The decision appeared to end a major battle in the continuing war between the government and the industry over auto fuel efficiency standards.

Transportation Secretary Brock Adams, in submitting the administration's fuel efficiency report to Congress, urged the auto industry to "join us, not fight us."

Adams conceded that the 27.5 miles-per-gallon standard for 1985 would be costly, but he said "those costs represent an investment in the U.S. economy. The cost of not meeting the standards means dollars being spent for foreign fuel -- and money in OPEC's pocket." OPEC is the Organization of Petroleum Exporting Countries.

The administration specifically rejected a proposal made last week by General Motors President E.M. Estes to phase in the new standard between now and 1988. Estes claimed this would save the consumer an average of $240 of the $590 per car he estimated the standard now will cost.

But Joan Claybrook, head of the National Highway Traffic Safety Administration, said yesterday that the GM plan would cost the nation an estimated 7 billion gallons of fuel during the proposed stretch-out period.

She also said fuel economy gained by the standards will save the average purchaser of a 1985 car " $500 in operating expenses over the life of the car."

The report predicted that implementation of the standards would permit a reduction in projected oil imports by 15 percent in 1985 and 20 percent in 1990.

Calling automotive fuel economy the nation's single most important energy-saving program, Adams said "through it, we can save 220 billion gallons of petroleum by 1990, save motorists $60 billion in unnecessary fuel costs in 1978 dollars, and reduce the trade deficit by $7 billion in 1985 and by nearly $12 billion by 1990."

Ford Motor Co. said it had "mixed feelings" about the Transportation Department report, and called on the agency "to scale back its overambitious goals and timetables."

Ford said that while "there is a lot to applaud in the agency's report," DOT underestimated some of the risks. For example, Ford said, "achievement of the present standards in the mid-1980s isn't assured at all -- even using diesel or alternative engines," because the technology may not now be in the hands of every domestic manufacturer.

The report said that "the fuel economy levels specified in the statute can be achieved by all domestic manufacturers without a significant change in the mix of their fleet and without a reliance on diesel engines."

Adams said achievement of the standards is "technologically feasible and economically practicable."

Adms and Claybrook said that meeting the requirements will provide the auto industry not just a challenge but an opportunity.

"Because they will be fuel-efficient, U.S. cars will, for example, be much more competitive on world markets," Claybrook said. "General Motors, for example, is already pushing for the creation of worldwide auto industry standards that will make U.S. cars more attractive around the world."

The report predicted, however, that from 1978 through 1984 the auto industry will have to invest $11.5 billion to achieve the standards. An economic downturn could thus pose "serious problems" for the industry, the report said, adding that DOT will assess such a downturn, if it occurs, to see if revisions in the standards are needed.