Eight automakers are keeping damage-resistant 5 mph bumpers on their 1983 models, but other manufacturers have put weaker bumpers on their cars since the government lowered its standards for bumper strength, the Center for Auto Safety reported yesterday.

Honda and Volvo have switched to weaker bumpers on all their cars and roughly half of all 1983 models have weaker bumpers that can result in higher accident repair costs, said center director Clarence Ditlow.

Bumpers on 1979 through 1982 model cars were required to survive a 5 mph collision with a fixed object without damage, but the standard was cut back to a 2 1/2 mph crash last July by the National Highway Traffic Safety Administration.

Ditlow said buyers of cars with the weaker bumpers face the possibility of "hundreds of dollars in damage in low-speed crashes," while those who buy cars with the stronger bumpers would get off easier.

Though automakers argued that lowering the bumper standard would save consumers money, Ditlow said his group found no evidence that they lowered their prices when they took off the 5 mph bumpers.

Chrysler Corp. equipped some of its early 1983 K cars with 5 mph bumpers, then switched to weaker bumpers for later production, Ditlow noted. There is no difference in the sticker price between the two versions and no difference in the outward appearance of the cars.

The only way Chrysler buyers can tell the difference is to look under the car to see whether the front bumper is held on by an energy absorber or a straight bracket, he added.

Ford said it is installing 5 mph bumpers on all its cars and plans to do so next year too. Other automakers using 5 mph bumpers on their full line include Toyota, Nissan (Datsun), BMW, Mercedes, Subaru and Saab. Volkswagen uses 5 mph bumpers on all its imported cars but puts 2 1/2 mph bumpers on made-in-America Rabbits.

Honda and Volvo switched to 2 1/2 mph bumpers on all cars and Chrysler put them on some models, the center found after asking car makers what kind of bumpers they were installing. American Motors and Renault are using downgraded 5 mph bumpers on all models built after Jan. 7. General Motors is using them on selected models.

Ditlow said he thinks car companies are not telling consumers which cars have which bumpers "because they are afraid it will adversely impact their sales if they have the poorer bumpers."

The center gave "good" ratings to those indicating they are using the 5 mph bumpers; "poor" ratings to those indicating use of 2 1/2 mph bumpers, and "inadequate" ratings to those who said they are using a modified bumper but failed to indicate the level of protection

Here are the Center for Auto Safety bumper ratings:

GOOD--Full 5 mph protection--All models of Ford, BMW, Mazda, Mercedes, Nissan, Saab, Subaru and Toyota. Volkswagen's Jetta, Quantum, Rabbit convertible, Scirocco, Audi 5000 and Audi Quattro. General Motors: Buick Electra and Skylark, Cadillac Cimarron and Fleetwood, Chevrolet Chevette, Corvette and Monte Carlo, Oldsmobile Omega, Cutlass Calais, Cutlass Ciera and Cutlass Crusier, Pontiac Phoenix and Bonneville; Chrysler Corp: Plymouth Grand Fury, Dodge Diplomat and Mirada, Chrysler Cordoba, Imperial, and New Yorker 5th Avenue.

POOR--2 1/2 mph bumpers--All models of Honda, Volvo, VW Rabbit (except convertibles) made after Jan. 10, 1983, Chrysler's Plymouth Horizon, Turismo and Reliant, Dodge Omni, Charger, Aries, 600 and 400, Chrysler LeBaron Sedan, New Yorkers E and Town & Country.

INADEQUATE--Degraded 5 mph bumpers--AMC/Renault all models made after Jan. 7, 1983, General Motors Cadillac DeVille, Brougham, Eldorado and Seville, Buick Century, LeSabre, Regal, Skyhawk, and Riviera; Chevrolet Camaro, Caprice, Cavalier, Citation, Impala and Malibu; Oldmobile 98, Cutlass Supreme, Delta 88, Firenza and Toronado; Pontiac Firebird, Grand Prix, 1000, 2000 and 6000.