The first launch of the space shuttle will be delayed five to six weeks because of the explosion last month of one of its engines during a ground test firing.

"We've suspended testing until we make some fixes in the engines we still have," space shuttle program manager Robert F. Thompson said at the Johnson Space Center. "But barring unforeseen difficulties we still think we can stick to the 1979 timetable and get the shuttle into orbit before the year is out."

The maiden voyage of the shuttle had been planned for Sept. 28, a date that is no longer possible because of the explosion Dec. 27 at the space agency's test center near Bay St. Louis, Miss.

The delay will be expensive, mostly because the shuttle payroll will have to be met for an additional five to six weeks before the first launch. The shuttle payroll runs $5 million a day. Each week's delay will cost the space agency $25 million.

The engine that blew up had been running for 255 seconds when a turbopump feeding oxygen to the combustion chamber overheated, caught fire and then exploded. The accident took place during the sixth firing of the engine.

Space agency engineers were that same day inspecting another engine that had been test-fired for 2,000 seconds. On breaking the engine down, they noticed that a metal sleeve between the valve and bellows in the pump was showing the telltale signs of wear.

"It was scratched and shiny from friction," Thompson said, "and on examining our other engines and the one that suffered the explosion we saw the same thing in all of them."

Thompson said that frictional overheating on some metal parts can cause the metal to burn. He said that engine experts have concluded that that was the cause of the explosion on Dec. 27.

The repairs that will have to be made to the engine to prevent a recurrence of the explosion are minor, Thompson said. The sleeve will have to be strengthened and built to have a tighter fit between the valve and bellows. All 12 engines will be repaired.

The space shuttle engine is the most advanced rocket engine ever built. Made to burn supercold liquid hydrogen and oxygen, the engine's high-speed turbine blades spin at 36,000 revolutions per minute. The amount of energy released during combustion in a single space shuttle engine is the equivalent of 60,000 horsepower.