SEATTLE (AP) _ The Navy rejected blimps as obsolete 25 years ago, but the dirigibles are on the way back, bigger and better, and plastics are what the Boeing Co. is counting on to make the difference in its bid for the contract.

Each blimp is projected to cost $66 million and is to be used for spotting and tracking Soviet sea-skimming missiles up to 125 miles away.

The blimps, which would be twice as long as Boeing's new 747-400 jumbo jets, would be cheaper than other airborne warning and control systems and less expensive to keep aloft, the company says.

The Navy is considering a fleet of 50 in a $3.3 billion program.

Boeing's $583,000 study contract produced a rigid body covered with plastics called composites, different from the more conventional soft bodies proposed by competitors Goodyear and Westinghouse, said Boeing Military Airplane Co. spokesman Richard Hill.

He said Boeing designers think the rigid material would be best because it could be repaired in flight and would be good for the uses planned for the blimp.

Dirigibles, first used more than 60 years ago, were very important during World War II but were abandoned by the Navy in 1961.

The newer versions would be much larger than previous models, capable of flying as high as 10,000 feet and at speeds of up to 100 miles per hour. The blimps would be made without metals so as to escape detection by enemy radar.

They could be equipped to launch missiles or warn other air and surface craft, via satellite, of attack.

The Boeing model would be 534 feet long, weigh 200,000 pounds and be about twice the size of Goodyear's blimp. It could cruise for as long as a month without landing, Hill said.

An interior support skeleton would carry a crew of up to 23 people. The crew would be housed inside the blimp rather than hanging in a gondola because of the need for the interior skeleton.

The type of engine hasn't been determined.

Goodyear builds blimps for advertising purposes. Westinghouse has joined with Airship Industries Ltd., a British firm that operates four blimps, also for advertising.