Lockheed Corp.'s prototype of a 21st century fighter jet made its first flight Saturday in a winner-take-all competition for the multibillion-dollar Advanced Tactical Fighter contract.

The YF-22 was airborne just 18 minutes, taking off from Air Force Plant 42 in Palmdale and ending 25 miles away at this desert flight test center.The flight was a milestone in a high-stakes contest between an aerospace team headed by Lockheed and a team led by Northrop Corp. for 1,250 ATF jets, to be built at a projected cost of $51 million per plane.

The winner must produce a jet that is highly maneuverable, uses radar-evading stealth technology and can fly twice the speed of sound for long periods of time. The Air Force wants 750 of the new planes and the Navy needs 500.

Pilot Dave Ferguson said the YF-22 flew as expected although the flight was shortened by 42 minutes because of problems at ground telemetry stations.

The jet burned so much fuel while sitting on the runway waiting for takeoff that there wasn't enough left for the scheduled one-hour flight.

"It was a very easy airplane to fly," said Ferguson, adding, "I would be happy to put fuel in it and fly it this afternoon."

The jet reached an altitude of 12,500 feet and a speed of about 280 mph. The two-tone gray jet with stubby wings and a V-shaped tail touched down smoothly in a light rain.

The YF-22 was built by Lockheed, General Dynamics Corp. and Boeing Co. It was unveiled in Palmdale Aug. 29, two days after the YF-23, built by Northrop Corp. and McDonnell Douglas Corp., made its first flight.

Lockheed Vice President Sherman Mullin, head of the YF-22 project, said he could not compare the two planes because he didn't have enough information about the YF-23.

Each team has spent about $600 million producing two prototype jets each.

"It's obviously an extremely important program to us," said Mullin. "(But) it's not a program that's going to make or break the Lockheed Corp."

Both planes are built of advanced composite materials. The Lockheed aircraft has stubby wings. The Northrop fighter has a longer, cigarlike fuselage and a wingspread that looks like a kite.

"This is a great day from a technological perspective," said Gary L. Denman, who heads an Air Force research division. "I can assure you, what's out there in the airplane is the best in the world."

Survival of the advanced fighter program was threatened by Congress until Iraq's Aug. 2 invasion of Kuwait. The crisis has enhanced prospects for approval of major defense contracts.

The $51 million cost of each jet is about twice that of the Air Force's present top fighter, the F-15 Eagle.