Donald D. Engen, who steps down this week as head of the Federal Aviation Administration, warned travelers yesterday that they will suffer more flight delays this summer but added there's not much the agency can do because there aren't enough airports to handle the increased traffic.

"I would take my wand and magically create four major airports," he said whimsically when asked what he would do in his final two days on the job to improve the situation.

Engen, a former Navy admiral and test pilot, said he would put those new airports in New Jersey, south of New York City, and near Chicago, Atlanta and Los Angeles.

In his last major public speech as FAA chief, Engen told a luncheon gathering at the National Press Club that the subject of aviation safety has not been well reported.

Paraphrasing a warning in May from the National Transportation Safety Board that there has been "an erosion of safety" in aviation, Engen said he sees "an unnecessary erosion of confidence" in air travel. That erosion, he said, can be blamed, in part, on the news media for oversimplifying a complicated issue.

Engen said that U.S. aviation is the safest in the world, adding that criticism of the system has often been based on "emotion and misinformation."

The FAA chief noted that his successor will never lack for people telling him how to do his job, and said, "There is a fine line between constructive oversight and unconstructive meddling."

Engen, a member of the NTSB before joining the FAA April 10, 1984, said too much emphasis has been placed on reports of near-collisions and controller errors. The NTSB, in its assessment of aviation safety, cited both as good measures of the margin of safety.

"Last year, controllers handled aircraft 94 million times with an error-free rate of 99.999 percent," Engen said. He added that the most definitive indicator of air safety is the accident rate -- and just as much emphasis should be placed on the statistics showing a decline in aviation accidents. Engen said the number of midair collisions has remained essentially steady over the past decade.

Engen, known for his soft-spoken style, said in a question-and-answer period after his speech that he had no problem getting along with Transportation Secretary Elizabeth Hanford Dole. He did not elaborate on his reasons for his retirement, other than to say, "There's never a good time to leave, but the time has come."

When Engen, 62, announced his retirement last March, it was widely speculated in aviation and government circles that he quit in frustration over the Transportation Department's interference with his management of the agency.

Engen's departure will leave the FAA temporarily leaderless. His successor, T. Allan McArtor, a former Air Force pilot and senior vice president of Federal Express, the air freight firm, was nominated by President Reagan June 6. His confirmation hearing before the Senate Commerce Committee is scheduled for Tuesday.

In his speech, Engen acknowledged that the rebuilding of the air traffic control system since the 1981 controllers strike has moved more slowly than he would have liked. But he said he wouldn't rehire any of the 11,400 fired controllers.

"The average age of the fired controllers in 1981 was 39," Engen said. "Today they are 44. It's a young person's game."

Engen also said he disagrees with the call to re-regulate the airlines.

"The airports today are the bus stations of the 1950s. You see people flying in cut-offs. You see people with babies on their backs. It is the U.S. flying," he said. Instead of re-regulation, he said, more terminals and more airports are needed to accommodate the masses.