TOKYO, DEC. 7 -- A step toward Japan's goal of developing an aircraft industry, three Japanese manufacturers have reached an agreement to take their largest role ever in development and production of a new U.S. jetliner.

Mitsubishi Heavy Industries, Kawasaki Heavy Industries and Fuji Heavy Industries reached a basic accord with Boeing Co. today under which they will jointly develop and make components valued at about 21 percent of the total cost of the airframe of the 777, according to Takayoshi Furuya, spokesman for Mitsubishi Heavy.

The twin-engine 777, a new 300-to-400-seat aircraft expected to be completed in 1995, is expected to compete against the McDonnell Douglas MD-11 and the Airbus Industrie A-330/340 in the market for long-range jets.

Japanese companies will also for the first time be involved in virtually every stage of development from design to airworthiness tests, financing and after-sales maintenance for the aircraft, Furuya said.

"We are not a full partner, but we are more deeply involved than before," he said. "We are a program partner."

Both sides declined to give the amount Japanese companies would invest in the project and which components each firm would produce.