The Pentagon disclosed yesterday that its explanation of the accidental bombing of a passenger train during the Kosovo campaign was flawed in one important respect: A videotape of the airstrike was shown to the public at nearly three times its normal speed.

But U.S. defense officials adamantly denied that the tape was sped up to make it appear that the pilot had no time to react to the arrival of the train on a bridge that was targeted for destruction.

Accelerated and compressed video images, normally used only for intelligence assessments, were inadvertently displayed at a NATO briefing because U.S. officials were in a rush to explain the accident and no one realized the tape was fast, said P.J. Crowley, a Defense Department spokesman. All the other bombing videos released during the Kosovo campaign were at normal speed, he said.

At least 10 people were killed on the train as it crossed the Grdelica ravine, 150 miles southeast of Belgrade, about noon April 12, Yugoslav officials said.

At the time, Serbia and the United States were locked in a public relations battle in several European countries, including some NATO allies, and the debate often centered on whether the United States was bombing recklessly.

The speed of events was a key element in NATO's explanation of the train bombing. At a news conference in Brussels the day after the accident, NATO's supreme commander, Gen. Wesley K. Clark, said the video demonstrated that the pilot of an F-15E fighter had aimed at an empty bridge and the train appeared so quickly that the crew had no chance to avoid it.

Describing what the jet's weapons officer saw as he guided an AGM-130 missile to its target, Clark said: "All of a sudden at the very last instant, with less than a second to go, he caught a flash of movement that came into the screen, and it was the train coming in. Unfortunately, he couldn't dump the bomb at that point. It was locked, it was going to the target--and it was an unfortunate incident which he, and the crew, and all of us very much regret."

The revelation that Clark used accelerated video images "in no way changes the basic facts that they were not able to divert the missile before the train came into their field of vision," Crowley said yesterday. If the tape had been played at real speed, it still would have shown that the weapons officer had just two or three seconds to react to the train, Pentagon officials said.

The jet, however, fired a second missile moments later. In his April briefing, Clark said smoke from the first missile had obscured the view, preventing the air crew from seeing the train with its engine ablaze.

Nearly all of the video footage that has become a staple of American air campaigns is processed by combat camera crews and shows events at normal speed, Crowley said. But, he added, intelligence technicians also convert the videotapes into computer data in a two-stage process that accelerates and compresses images. The result is video that runs at 2.7 times real speed and that easily can be downloaded into a personal computer. The computer files are analyzed to determine whether airstrikes destroyed their intended targets, Pentagon officials said.

When Clark started the April 13 briefing, he told reporters that the videotape of the train was "hung up in a computer problem." Then, as the briefing was about to end, he displayed the footage.

The Pentagon revisited the matter yesterday in response to allegations in a German newspaper that the video images had been manipulated. "The heart of this is simply whether this video was manipulated, and our answer is no, it was not, definitively not," Crowley said.