Air Force Gen. Richard Myers conceded to the Senate Armed Services Committee that the military didn't get any fighters into the air until after the second World Trade Center tower was struck, revising an earlier statement that they didn't lift off until far later, after the Pentagon was attacked.

''What happened to the response of the defense establishment?'' Sen. Bill Nelson, D-Fla., asked Myers at his confirmation hearing.

Myers said that after the second tower was hit, he spoke to NORAD's commander, Air Force Gen. Ralph E. Eberhart, ''and I think the decision at that point was to start launching aircraft.''

Col. Mike Perini, a North American Aerospace Defense Command spokesman, said Tuesday night that fighters were ordered to intercept one of the airliners that hit the World Trade Center. However, he said, the jets were just lifting off when the airliner struck.

And there were no military planes in the skies over Washington until 15 to 20 minutes after the Pentagon was hit - some 40 minutes after the second New York tower was attacked, a defense official said, speaking on condition of anonymity.

The rest of the day, the military was on high alert. A false alarm of a hijacking of a KAL flight from Korea to the United States sent fighters scrambling to keep it out of U.S. airspace, which had been closed to all civilian air traffic.

Myers cited one cause of delay in the initial response: ''We have many fewer aircraft on alert than we did during the height of the Cold War.''

''It's not just a question of launching aircraft, it's a question of launching to do what?'' he said. ''You have to have a specific threat. We're pretty good at threats from outside, we're not so good at threats coming from inside.''

Myers confirmed rumors about a fifth plane that was headed toward the United States on Tuesday with a report of being hijacked.

The plane's transponder indicated by code that it had been hijacked, but after U.S. fighters steered it over Alaska and the plane landed safely in Canada, it became clear there had been no hijacking, Myers said. The second defense official identified it as a KAL aircraft.

''I don't know ... whether it was a mistaken switch setting or what,'' he said, but asserted, ''The plane was not hijacked. ... We had other things to do at that time, and once it was safely on the ground, the passengers were safe, we went onto the next order of business.''

Myers said he knew of a report of another aircraft headed to the United States that was called back by its company and returned to Europe.

He rejected rumors that the military shot down the hijacked plane that crashed in Pennsylvania.

''The armed forces did not shoot down any aircraft,'' Myers said. ''When it became clear what the threat was, we did scramble fighter aircraft, AWACS radar aircraft and tanker aircraft to begin to establish orbits in case other aircraft showed up in the FAA (Federal Aviation Administration) system that were hijacked, but we never actually had to use force.''