Gen. Lew Allen Jr., a former Air Force chief of staff, was misidentified yesterday as a former Air Force secretary in an article about the search for a new administrator for the National Aeronautics and Space Administration.

The White House, searching for a new administrator to lead the National Aeronautics and Space Administration through its most difficult time in many years, is still focusing on James C. Fletcher, who retired from the job in 1977, a White House official said yesterday.

Fletcher, however, has said repeatedly in public that he does not want the job. If he cannot be persuaded to accept it, the backup candidate is Gen. Lew Allen Jr., former head of the Air Force, a senior administration official said.

"Fletcher is the choice if he's willing to take the job," the White House official said.

He added that President Reagan had not yet made a formal decision and that neither the president nor his chief of staff, Donald T. Regan, had called Fletcher.

Fletcher could not be reached for comment yesterday.

The current head of NASA, William R. Graham Jr., was appointed acting administrator two months before the Challenger explosion, after James M. Beggs stepped aside following his indictment on charges unrelated to NASA.

Fletcher presided over NASA from 1971 to 1977, the years that saw the last of the moon landings, the Earth-orbiting Skylab program and the Soviet-U.S. joint flight in Earth orbit.

Allen, who was secretary of the Air Force from 1978 to 1982, helped create the U.S. Space Command, an interservice administrative center in Colorado Springs that oversees military uses of space.

Sen. Jake Garn (R-Utah), chairman of a subcommittee on space budgets, has been pushing for Fletcher. But an aide to Garn and other sources in the House and Senate said yesterday that both Fletcher and Allen are highly regarded and either would be acceptable.

The only reservation expressed was about Allen's military background. Richard H. Truly, recently appointed head of the shuttle program, is a rear admiral and Graham worked in weapons systems.

It was suggested that an administrator with similar orientation would fuel existing concerns that NASA has been taking on too much military coloration for a civilian space agency.

Harrison H. (Jack) Schmitt, former geologist-astronaut who explored the moon and a former Republican senator from New Mexico, has been mentioned as a candidate for the administrator's job, but sources said he is not high on the list.

Meanwhile, at a breakfast for reporters yesterday, Reagan repeated his vow to keep the shuttle program going despite evidence that NASA has a flawed process of deciding whether a shuttle launch will be safe. Last week the presidential commission investigating the Challenger disaster found that top NASA officials were never told of warnings the night before the launch that it was dangerous to fly in such cold weather.

"Whether it was intentional or not," Reagan said, "there were ways in which counsel and advice in regard to the safety factor could be ignored and the launch took place with the tragic follow-up."

"Now, I don't know whether there was any intent or whether anyone knowingly just gambled and took a chance or whether it was just error in judgment. But that's what we're going to find out with this commission report," he said.

The president said he wanted to see changes to assure that "this sort of thing can never happen again."

In another development, the Associated Press reported that some members of the presidential commission were surprised to learn Tuesday that NASA "cannibalized" parts from its four shuttles to make one shuttle ready for flight.

On each flight, according to the report, an average of about 10 percent of the orbiter's parts came from other ships.

Jim Mizell, NASA spokesman at Cape Canaveral, said this has been "routinely done" but only with the orbiter itself. It was decided early in the program, he said, not to build orbiter spares because "we didn't know what the final orbiter would look like."

It was considered the "most cost-effective way to do business," Mizell said.