Yesterday was a bad day for the auto industry.

The National Highway Traffic Safety Administration issued a preliminary finding that 1.9 million Ford Pintos and 30,000 Mercury Bobcats built between 1971 and 1976 have serious fuel system defects that can lead to fires during rear-end collisions.

In addition, NHTSA, an arm of the Department of Transportation said that the 1977 Chevrolet Chevette does not comply with federal safety standards for its fuel system, which the agency said "is not secure from rupture and leakage."

And finally, Ford Motor Co. documents released in Detroit yesterday reveal that alleged safety defects in Ford transmissions may have been responsible for at least 277 accidents involving 100 injuries and 9 deaths since 1966.

Those documents were released at the request of NHTSA, which is investigating reports that some Ford automatic transmissions have slipped from park into reverse, sometimes resulting in the driver being crushed by his or her own car.

At least 49 lawsuits have been filed against Ford in connection with the transmission problem, but Ford Spokesman said company engineers have found no safety defects in the cars, suggesting instead that the accidents were caused by human error.

The Pinto/Bobcat fuel tank ruling sets in motion the mechanism by which the Department of Tranportation can order a former recall.

NHTSA administrator Joan Claybrook said that Ford, or anyone else, had 30 days to review the evidence presented by the agency, and that there would be a public hearing here June 14.

Safety administration spokesmen said their agency has received reports of 38 fires, with 27 fatalities and 24 non-fatal burns, resulting from Pinto rear-end collisions. Although no reports had been received on Bobcats, the cars are extremely similar.

A Santa Ana, Calif., jury recently awarded a record $128 million to a teen-ager in Santa Ana, Calif., who was burned critically in a Pinto, rear-end collision that resulted in a fire killing the driver of the car. The youth has since agreed to a reduced award of $3.5 million, but Ford is appealing the verdict.

The Chevette problem concerns new standards set by NHTSA for vehicle safety. The rules went into effect for 1977 models, and NHTSA tests revealed that the Chevette and Ford Granada fuel systems were not secure from rupture and leakage in a 30-mile-per-hour rear-end impact accident.

Ford recalled the Granada for the problem, but General Motors challenged the NHTSA test, disputing the manner in which it was conducted.

That was 10 months ago. Since then, NHTSA has run four or five more tests and has come to the same conclusion, according to Claybrook.

NHTSA has schedule a meeting on June 6 for GM to present its objections publicly.