Crash tests on two 1981 cars -- a Ford EXP subcompact and an Audi 5000 compact -- were invalidated yesterday by the National Highway Traffic Safety Administration, as the agency announced it would take a hard look at this part of its consumer information program.

NHTSA Administrator Raymond A. Peck said apparent defects in the test procedures had cast doubt on the results for these two cars. The EXP and the Audi failed to meet the passenger safety criteria set by NHTSA for its comparative crash tests, according to results, released this weekend.

In a statement yesterday, Peck said NHTSA hasn't decided whether to retest the EXP and the Audi 5000. They were among 15 new models given special comparative crash tests by NHTSA in the latest round of the two-year-old program.

In the tests, the cars are rammed into a fixed wall at 35 miles an hour, and the crash forces are measured on dummies restrained in the front seats by standard seat belts and shoulder straps.

An American Motors Corp. Spirit, a two-door Chrysler Imperial, and a two-door Honda Civic were the only cars that were within the permissible crash force limits set by NHTSA in head-on collisions, although the agency pointedly declined to say that the three cars had "passed" and the rest had "failed." In the Carter administration, NHTSA had applied pass-fail ratings to all the new cars undergoing the comparative crash tests.

In addition to invalidating test results on the EXP and the Audi cars, Peck said he wants to repeat a series of tests on the same kind of car, to see if the crash impact numbers registered by the "driver" and "passenger" dummies are consistent.

The auto industry has attacked the comparative crash test program, saying that there is considerable variation in results.

Peck said that results on different cars of the same model could occur because of differences in the way the cars are manufactured, how the cars are equipped, and in the test conditions themselves.

Peck himself detected one such problem in test conditions involving the EXP. A film of the EXP test crash shows the "head" of the front seat passenger dummy slamming into the dashboard with enough force to cause serious injury or death in a human, as the numerical readings from the dummy showed, NHTSA said.

Such a finding would have probably plunged Peck into a serious dispute with Ford, which needs strong sales of the EXP as it tries to recover from its heavy financial losses.

Peck decided to scrutinize the film Friday evening, and he said he saw that a piece of adhesive tape connected to the passenger dummy's shoulder belt failed to release on impact, as the test procedure called for. This may have produced invalid results, Peck said, by pulling the shoulder belt out of its proper place, permitting the dummy to strike the dashboard with such force.