EDWARDS AIR FORCE BASE, CALIF., AUG. 27 -- A team from Northrop and McDonnell Douglas today became the first aerospace firm to fly its version of the Air Force's Advanced Tactical Fighter.

The twin-engine YF-23 took off this morning and joined two chase planes on a flight that lasted about 50 minutes.

Developed jointly by Northrop Corp. and McDonnell Douglas Corp., the fighter is designed to evade radar and to maneuver at supersonic speeds for long periods of time. Pratt & Whitney, a unit of United Technologies Corp., built the engines.

Today's flight of the YF-23 upstaged Wednesday's scheduled rollout of the YF-22, a competing version of the ATF built by Lockheed Corp., Boeing Co. and General Dynamics Corp.

The two aerospace teams are competing for a multibillion-dollar Air Force contract to produce 750 of the fighters. The ATF will cost about $51 million per plane, almost twice as much as F-15 Eagles, the Air Force's current top fighter.

Each team has spent about $600 million on producing two prototypes each. The Pentagon has matched the funding.

The Air Force says the futuristic fighters, which would replace the F-15 Eagle, are needed to maintain air superiority.

"We've never fought a war where we didn't enjoy air superiority," Brig. Gen. James A. Fain Jr. had said before the Iraqi invasion of Kuwait.

Northrop spokesman Tony Cantafio said there was no connection between the decision to put the YF-23 into the air and attention to military matters due to the Middle East crisis. "This is a coincidence. They fly when they're ready to fly," Cantafio said.

If Northrop and McDonnell Douglas win the contract, it would bring thousands of jobs to California. The Lockheed-Boeing-General Dynamics team would build the planes in Georgia.