Two weeks before the crash of TWA Flight 800, the inspector general for the Department of Transportation completed a report on airport security that described how undercover government agents had been able to breach security at four of the nation's largest airports.
The agents got into secure areas that would have given them access to airplanes. Some of them carried fake bombs.
The report showed that agents carrying the fake bombs, and others participating in the investigation, were successful in their efforts to sneak past security checkpoints in 40 percent of their attempts, which occurred in 1995 and early 1996.
Government investigators reiterated Friday that they still did not know what caused the crash of the TWA plane. But the idea that it was brought down by a bomb is a leading theory.
The inspector general's report was a follow-up to a similar inspection of the same four airports in 1993 in which agents were able to get into secure areas and sometimes onto airplanes in 15 of 20 attempts _ 75 percent of the time.
"Once we gained access, we wandered around aircraft parking areas, baggage processing centers, maintenance areas and ramp administrative offices," the 1993 report said.
The agents in that inquiry also managed to get onto planes _ one of them entering a cargo hold and another entering the cabin of a plane and leaving a note to prove he was there.
"During our tests, we displayed no visible identification, dressed casually, engaged in behavior designed to elicit challenges and did not resort to covert methods," the report said.
Mary Schiavo, who resigned as inspector general July 8, said Friday that she had wanted the report released quickly in an edited form. But she added that the Federal Aviation Administration and other security officials decided not to make it public because they were concerned that it might help any terrorists who intended to sabotage airplanes during the Olympics.
Bill Schulz, a spokesman for the Department of Transportation, said that on July 9, the day after Schiavo left office, the deputy inspector general wrote a memo about the report to the secretary of transportation.
Schulz paraphrased the memo as saying that "for security reasons, we will not release this report at this time." He declined to say whether the Olympics played into the decision, adding only that security officials believed releasing the report would be "damaging to national security."
Schulz said that no decision had been made on when the 1996 report would be released but that officials would try to release it "within the same rough time frame, if not sooner, than the previous reports." He said that in 1993, it took more than two months from the time of the report's publication to release of the report in its edited form.
The government official's description of the 1996 inspection report suggests that airport security has improved in the past three years, since agents were able to get through security checkpoints less often.
But in 1996, the agents also tried different methods of breaching security and placed emphasis on trying to smuggle in fake bomb parts, officials familiar with the report said.
The descriptions of the 1996 report did not make it clear whether the agents carried the fake bombs onto planes, or stopped their efforts after making it through the X-ray equipment, into areas that could have given them access to the planes.
Schulz said the memo from Deputy Inspector General Mario Lauro to Transportation Secretary Federico Pena on July 9 said that "since our prior audit in 1993, the FAA significantly improved its approach to oversight of airport and air carrier security programs."
At the same time, though, he added that the memo also notes "shortcomings in both airport and air carrier security programs."
Ms. Schiavo said Friday that unedited version of the report arrived at her office July 3 and that she had been in favor of releasing an edited version soon afterward. She said that FAA and Transportation Department officials had told her they were concerned about the timing of the release.