Two of the space shuttle Challenger's main engines were removed for repairs at Cape Canaveral yesterday, and the third was being brought from Mississippi for similar maintenance.

Technicians will cut away a metal sleeve that acts as a shock absorber for an injector (carburetor) head feeding hydrogen to a small igniting chamber that initiates combustion in the engines. Once the sleeves on all three engines are cut away they will be repaired and strengthened and put back on the injector heads.

Cracks were discovered in sleeves on the two engines at the cape after the engines developed fuel leaks in tests. While no cracks were found in the engine that is being trucked to Florida from Mississippi, it will be strengthened to make sure it does not develop a crack in flight.

NASA said yesterday that the removal, repair, retesting and reinstallation process for all three engines will take from one to two weeks. "If you had to set a new launch date right now, I'd say you'd be best off with March 29," a spokesman said.

This is the fourth delay of Challenger's maiden flight, which will be the sixth by a space shuttle. All four delays were caused by leaks in the three liquid hydrogen engines that will power the 100-ton spaceliner into orbit after its two solid rocket boosters burn themselves out.

Challenger's engines are more powerful than Columbia's, having a thrust potential of 104 percent. This lets Challenger lift more weight into orbit, a task it will have on its first flight, when it will carry a 25-ton satellite called the Tracking Data and Relay Satellite into space.