Thousands of students at the Federal Aviation Administration's air traffic control academy in Oklahoma City had access to a widely circulated "cheat sheet" for the final exam, according to federal investigators.

A recently concluded investigation by the Transportation Department's inspector general found that materials nearly identical to problems used on the final exam have been circulating among students since July 1986 and may have been generally available to students since 1982.

"The exercises were given from student to student, from class to class, from air traffic control graduates to new students and from personnel at air traffic sites in FAA regions to regional candidates about to be sent to the academy," Inspector General John Melchner said in a memo to the FAA.

Investigators were unable to determine how many, if any, students who might otherwise have failed the exam passed with the help of the materials. Melchner noted in his report that management at the academy did not think the test questions had been compromised.

"Instructor cadre, on the other hand, have told us that the disseminated test materials are so specific and represent the graded exercises in such fine detail that they consider the nine graded exercises to be compromised," Melchner wrote.

Some instructors were concerned that the widespread use of the materials will hinder the program at a time when the FAA is under pressure to train hundreds of new air traffic controllers quickly. By using the materials, marginal students may have been able to continue to the next stage of training, costing the FAA time and money, when they should have been weeded out of the program.

After leaving the academy, student controllers must successfully complete another 2 1/2 years of on-the-job training and pass 10 more exams before they are considered fully trained.

Since 1982, the nine-week basic air traffic controller class has been taken by 17,333 trainees. Of them, 10,172 -- or 58.7 percent -- passed the exam. Under normal circumstances, 60 percent of every class passes the final exam.

In three classes enrolled in the academy last fall -- when the materials were believed to be most widely circulating -- a larger proportion of students passed the final exam. In the September class, 68.8 percent of the students passed; in the November class, 72.1 percent of the students passed, and in the December class, 69.1 percent passed.

Douglas R. Murphy, manager of the academy's air traffic branch, said the students in those classes scored higher because they had higher than average scores on a previous screening test and were six months younger than average students. Academy psychologists say younger students tend to score higher on tests.

Murphy said the compromised problems have been replaced and that the pool of test problems will be expanded to 90 problems to make it more difficult to cheat.

Incoming students are now asked to sign an acknowledgment that that they will be fired from the FAA if they are caught cheating.