Compliance with the 55 mile-an-hour national speed limit is down sharply these days. In the decade since the law took effect after the 1973 Arab oil embargo, Americans have been stepping a little harder on the gas pedal. Motorists now average just over 59 miles an hour.
Although state police often give drivers a five-mile-an-hour leeway when it comes to stopping speeders, federal rules allow no such variation. To qualify for a substantial portion of highway trust funds, states must certify that at least 50 percent of their motorists are keeping within the 55-mile limit. Going 56 miles an hour is considered as much out of compliance as going 70.
Washington now estimates that as of Jan. 1, when state reports on the last year's compliance are due, Arizona, Maryland, Vermont, and possibly Oklahoma will fail to meet federal standards.
In February Congress will take up the issue of whether or not there should be a change in federal compliance rules in February. The House is scheduled to hold hearings then on a two-year, congressionally ordered study by a committee of the National Research Council (NRC) of the costs and benefits of the national speed-limit law.
Those who want to see a change, including the authors of the NRC report, say a system that penalizes states more heavily for motorists traveling at higher speeds would be more appropriate. It would also be more in line, they say, with state enforcement practices, which often peg fines to the speed traveled.
Also up for consideration at the February hearings will be the question of whether to allow an exception to the 55 m.p.h. limit along sparsely populated rural stretches of Interstate highway (70 to 75 percent of the system). Many drivers who spend long hours on the highways, particularly in the West, say an exception makes sense.
''We consistently hear very positive things from people in the East, where the limit saves proportionably more lives, and great concern and not a little anger from motorists in the West - it's an entirely natural reaction,'' says John Archer, government affairs director of the American Automobile Association (AAA).
Those who want a change feel they have limited ammunition, of sorts, in the new NRC report. While carefully making no recommendations - insisting that any decision would be political rather than scientific - the committee concludes that higher speed limits on rural Interstates could have strong benefits without a ''proportional'' impact on safety.
An estimated 100 years of travel time, for instance, could be saved for every highway fatality, according to the report.
But the panel estimates that raising rural Interstate speeds to 60 or 65 would result in some 500 more fatalities a year and burn 10 million more barrels of fuel.
And any move to shift speed limits by handing power back to the states would be hotly controversial. Many argue, for instance, that once allowed to go faster anywhere, motorists might be inclined to carry that habit with them. Safety experts call it the ''psychological spillover'' effect. And William Haddon, president of the Insurance Institute of Highway Safety, an independent research group, argues that many of the nation's Interstates, although often designed for speeds above 55, are ill-equipped - particularly along highway shoulders - to handle crash speeds above that limit. Dr. Haddon notes that the Rocky Mountain states, while often critical of the national speed limit, have ''by far'' the worst record for highway deaths and injuries.
A number of safety experts say nothing more is needed than a stronger crackdown on speeding motorists. By most estimates the 55 limit saves 2,000 to 4 ,000 lives and as many serious injuries a year.
''We're losing some of the benefits (of the speed limit) now because it isn't being enforced well,'' insists Charles Hurley, executive director for federal affairs of the Chicago-based NSC.
The AAA's Mr. Archer insists that unrealistic federal compliance laws now encourage states to concentrate enforcement on safer Interstates where volume is high, rather than on roads where speed-limit excesses are often greater and more dangerous. ''It rewards states that try to slow the whole compliance stream,'' he says.
But Harold Thursby, a highway safety specialist with the National Highway Traffic Safety Administration (NHTSA), reasons that Interstates, as the most traveled highways, are the logical place for states to put ''the lion's share'' of their enforcement efforts.
Much now depends, experts say, on how the administration comes down on the issue. In the opinion of the NSC's Mr. Hurley, the Reagan administration so far has sent the ''wrong message'' to motorists by its early ''open hostility'' to the 55 mile-an-hour limit (through high-level public comments and the 1980 Republican platform urging the limit's repeal) and by its more recent ''benign neglect'' of the issue. But he says US Transportation Secretary Elizabeth Dole has done a good job. He hopes that she will help bring about a change in the administration's position. Officially the NRC report is still ''under study,'' according to NHTSA's Mr. Thursby.