Proponents of lower fuel-economy standards are already at work trying to persuade the National Highway Traffic Safety Administration to reduce requirements for the 1987 through 1989 model years.

The NHTSA agreed this week to a request from General Motors Corp. and Ford Motor Co. to lower the standard from 27.5 miles per gallon to 26 mpg, but only for 1986 models.

GM, Ford and a host of foreign-car manufacturers that will benefit from the rule gave the NHTSA lukewarm applause. But, almost before the ink had dried on the regulation, the automakers' lobbying group, AutoChoice, was busy churning out press releases seeking a more extensive rollback.

The NHTSA's "common-sense adjustment for one year is a welcome adjustment," said Jeffrey Conley, executive director of AutoChoice. But he cautioned his clients "not to breathe a sigh of relief."

"The same kind of adjustment is necessary for future years to avoid economic hardship to the domestic auto industry," Conley said. "One year of relief is not enough."

"The "economic hardship" reference was to the revenues and jobs that GM and Ford say will be lost in the United States if they are forced to curtail production of big cars to meet higher corporate average fuel economy (CAFE) standards in the future. The standards establish average "feasible" fuel-economy levels for all cars in new-car fleets sold in the United States. Automakers whose fleets contain a large proportion of big cars tend to receive lower ratings.

Still, the "economic hardship" argument raises an interesting question. Both GM and Ford, as well as West European manufacturers such as Daimler-Benz Inc., were well into 1986-model production when NHTSA issued its ruling. That means their big cars were already rolling out of the factories on the way to showrooms. What would those companies have done if NHTSA had decided to stick to its guns and stay with the 27.5 mpg standard for 1986?

The betting in Detroit, particularly in the corridors of Chrysler Corp., which has long opposed a rollback of the full-economy standard, is that GM, Ford, et al. would have sold the cars anyway -- without incurring potentially hefty fines attached to violations of the standards.

The same folks are betting that NHTSA will find an excuse -- the agency also cited potential economic hardship this time around -- to relax the standards for the next two or three model years.

But the NHTSA officials insist that they have not made any decisions about the future, and that those matters are still under study.