WASHINGTON (AP) _ It started with a telephone call from a friend of one of America's most famous families: A plane carrying John F. Kennedy Jr., the anxious caller said, was past due at the airport.

With that report, made about 2:15 a.m. Saturday to the Coast Guard station in Woods Hole, Mass., the military hierarchy sprang into action and started a desperate search for the son of a former commander-in-chief.

Crews in Woods Hole contacted the Federal Aviation Administration, according to Coast Guard Rear Admiral Richard Larrabee. The FAA, charged with supervising the nation's air space, in turn started calling airports and flight-tracking centers up and down the East Coast.

Kennedy's plane, a Piper Saratoga II HP carrying him, his wife, Carolyn Bessette Kennedy, and her sister Lauren, had left Fairfield, N.J., Friday evening. It was due into the airport at Martha's Vineyard, Mass., well before midnight. Airport officials said it never arrived.

As it called its own personnel, the FAA also placed call to the Air Force Rescue Coordination Center at Langley Air Force Base in Hampton, Va., the elite unit that coordinates searches throughout the country.

By 3:30 a.m., Larrabee said, the unit called back to the Coast Guard and reported a satellite had received a signal from an emergency locator beacon over land on the northern end of Long Island.

Larrabee said a boat was sent to the area but did not find anything during a three-hour search.

At 7:30 a.m., Larrabee said ``a more aggressive search'' was launched. A Coast Guard jet was dispatched to the skies over Long Island Sound. Two Coast Guard helicopters were launched to search between Martha's Vineyard and Montauk, N.Y.

An Air Force C-130 was transformed into an aerial command post and sent to southern Long Island. Within hours, 15 more small planes manned by volunteers from the Civil Air Patrol, the Air Force auxiliary organization, also were buzzing over the coastline.

By 1 p.m., the search parties zeroed in on a spot 17 miles southwest of Martha's Vineyard, after swimmers found a suitcase bearing Lauren Bessette's luggage tag floating in the surf off Philbin Beach.

The Pentagon said the sizable search had nothing to do with Kennedy's status as the only son of the late President John F. Kennedy.

``We treat all the searches the same,'' said Lt. Col. Steve Roark, an official at the Air Force rescue center. ``There is no difference between celebrity and noncelebrity. Our job is for all the citizens of the United States.''

Officials also defended the four-hour time lag between receiving a report of the missing plane and launching a more intensive search.

``It does take time to research. We look at possible other landing sites ... rather than just sending out aircraft willy-nilly,'' Roark said.

Larrabee said rescuers were hampered by the fact that Kennedy did not file a flight plan for his trip, which was not required.

``At this point we didn't have any better information because we did not have a flight plan,'' Larrabee said, recalling the early morning hours. ``We had a time of departure but did not have any other good information, so we found ourselves searching a very large area.''

Larrabee said the searchers planned to continue until they found the aircraft.

``The weather is really not a factor,'' he said.

Rescuers hoped an incoming boat from the National Oceanic and Atmospheric Administration would lend assistance. The vessel, which had been off the coast of Long Island, is equipped with sonar allowing undersea searches.