Members of a House subcommittee yesterday denounced Lockheed Corp. for the apparently widespread loss of classified documents involving a supersecret Air Force jet-fighter project and charged that company employes falsified evidence to cover up the possible damage to national security.

The missing items, which General Accounting Office officials testified may involve more than 1,000 secret documents, film and other material, were described by panel members as potentially the most serious abuse they had yet encountered in their ongoing probe of defense contractors. Subcommittee staffers identified the documents as relating to the Air Force F19 "Stealth" fighter -- a so-called "black" or classified program that the Pentagon has never admitted exists.

Meanwhile, the Pentagon, which is conducting its own investigation of Lockheed's handling of the documents, yesterday said it is currently "impossible" to determine if there has been any breach of national security because it has no way of knowing whether any of the missing documents have been obtained by hostile foreign powers.

"The fact is, we don't know what's gotten out," said Rep. Ron Wyden (D-Ore.) during a hearing of the House subcommittee on oversight and investigations. "We don't know if the Soviets have gotten anything. We don't know if terrorists got anything. . . . We have had a total breakdown of the system."

"It does look to me like some sort of public or private hanging should take place over this," subcommittee Chairman Rep. John D. Dingell (D-Mich.) told Lockheed Chairman Lawrence O. Kitchen at the hearing.

While repeating the company's previous statements that there is no evidence of an actual compromise of security, Kitchen said that he was "embarrassed" by his firm's inability to locate the missing documents and that it was "outrageous" that some documents are known to have left a Lockheed plant.

Under tough questioning by panel members, he also acknowledged that some company officials may have backdated audit forms claiming that some classified documents were destroyed years ago in an improper attempt to account for missing material.

"There may have been backdating," said Kitchen. "There's a difference of opinion as to whether this was a cover-up or whether this was just bad management."

Kitchen's comments came after GAO officials testified that, during an audit last month of Lockheed's California operations, company officials were initially unable to locate 1,460 classified documents involving the secret Air Force project. As of last week, Lockheed had conducted a thorough investigation of 235 of these documents and was able to account for 224 of them, with 11 listed as "unresolved," meaning that "all logical leads have been exhausted."

Martin Feber, GAO associate director of the national security, said the proportion of "unresolved" documents can be expected to grow significantly since the company's initial investigation involved documents considered the easiest to locate.

Panel members, however, became even more irate after two Lockheed security officials testified that middle-level Lockheed managers had concealed the missing documents by preparing audit forms asserting they were destroyed years ago. John P. Kolbach, one of the security officials, said that he was personally instructed to sign a "destruction-request" form stating he witnessed the destruction of some documents on July 15, 1982 -- more than a year before he joined the company.

Kitchen said that there is no evidence of "an intent to deceive" by Lockheed officials, but that the firm was continuing its own investigation into the preparation of the forms. Subcommittee members, however, demanded to know why the Lockheed chairman had failed to take disciplinary action.

"For the life of me, I can't see why somebody hasn't been demoted or fired," Wyden said.

Wyden and others said the breakdown in controls at Lockheed pointed to the need for greater congressional scrutiny of classified programs.