The near collision of Vice President Bush's Air Force jet with a single-engine plane Thursday near Seattle apparently occurred because the small plane's pilot failed to notice the approaching jet, Federal Aviation Administration sources said yesterday.

An air traffic controller helped avert a collision when he told the pilot of Air Force Two by radio to be on the lookout for another plane in the vicinity, FAA spokesman Ed Pinto said.

The two planes came within about 200 feet horizontally before Air Force Two's co-pilot took command and dropped a few hundred feet to avoid the small plane, said Liz Grundy, speaking for Bush's office.

The FAA and the National Transportation Safety Board are investigating. The Air Force pilots did not file a formal report with either agency, officials said.

The near miss "shouldn't have happened. It's not to be diminished," Pinto said. "We consider it to be serious."

The small craft, not identified by the Air Force pilots but described as green and white, was equipped with a transponder, a device that signaled its location but not its altitude to a controller's radar screen at Seattle-Takoma Airport, Pinto said.

A few minutes before the near collision, the controller notified the Air Force Two pilot that the plane was two miles away "and told him to start looking at 10 o'clock," Pinto said.

The near collision occurred at 2,600 feet as Air Force Two -- carrying more than 25 Bush staff members, reporters and Secret Service agents -- was descending northwest toward Boeing Airfield, seven miles away.

Air Force Two's co-pilot spotted the plane heading northeast almost straight toward the jet, and took the jet into a dive, Bush staff members said. Drinks spilled in the front cabin where Bush was sitting, Grundy said, adding that the vice president noticed the drop but "seemed unconcerned."

"You're talking to an old Navy pilot, where we used to fly wing-to-wing, the guys' wingtips almost touching," Bush told reporters later. "Two hundred feet? That seems like a mile to me."

The small plane passed 300 to 500 feet over Air Force Two, Pinto said.

It was the second near mishap for Bush's plane in three weeks. On Sept. 30, Air Force Two, a modified Boeing 707, came within three-fourths of a mile of a twin-propeller plane outside Cleveland. FAA sources said this apparently was the result of a controller's error.

Pinto said there is no requirement at Seattle-Takoma Airport that a private pilot communicate with controllers or maintain a set distance from other planes.

FAA sources said the near collision again raises questions about the safety of some small business and pleasure planes not in contact with controllers. An FAA report released this week said that 92 percent of near collisions involve such light aircraft.

FAA officials added, however, that the Aircraft Owners and Pilots Association, which represents these pilots, has stepped up its campaign to remind members to "see and avoid."

The FAA said the number of near collisions has declined for several years, from 586 in 1980 to 286 last year.