Pratt and Whitney, the engine manufacturing subsidiary of giant United Technologies Corp., has scheduled a major news announcement for Wednesday that aviation industry sources predict will herald the launching of a new jet engine.

According to published reports, Pratt and Whitney will announce plans to test a highly fuel efficient turbojet engine developing 60,000 pounds of thrust for use on planned "stretched" versions of jumbo jetliners. It would be the largest engine ever built and would be the result of lower-cost manufacturing technology.

The largest engine currently manufactured, the Pratt and Whitney JT9D-74R develops 54,750 pounds of thrust and is an option on the new Boeing 747 with an extended upper deck.

That engine "probably has the capacity to be expanded to 60,000 pounds," a federal source said. He suggested such an engine could be used on a double-deck Boeing 747 currently being discussed with the Japanese. The engine on a typical Boeing 727, the most common jetliner, develops 16,000 pounds of thrust.

The Hartford Courant has reported that Pratt and Whitney is planning the huge new engine. A Pratt and Whitney spokesman declined to comment on the story, calling it "speculative."

However, he said Wednesday is the 10th anniversary of Harry J. Gray's assumption of the presidency of United Technologies, where Gray is chairman and chief executive officer. "We are having a tribute to Mr. Gray and a news announcement," the spokesman said. Major airframe manufacturers and selected journalists have been invited, he said.