He was almost furtive in his tour, slipping into the exhibition the wrong way around - beginning at the end. He studied several photographs and read some of the captions.

If he had not remarked on an error in one display last night - 10 years after Apollo 11's historic jounrney to the moon - former astronaut Michael Collins, now undersecretary of the Smithsonian Institution, might have been just another space fan at the Library of Congress, nondescript and uncommunicative.

Was it nostalgic, he was asked, to see photographs of himself and fellow astronauts Neil Armstrong and Edwin Aldrin Jr. on their mission to the moon?

"Oh, of course it's nostalgic," Collins began, then drew himself up short. "But I'm not giving any interviews. We've all had so many requests."

He drifted off past the library's effort to trace, through documents, photographs, taped commentary and speeches, how it was that America walked on the moon.

Upstairs, at a reception marking the exhibit opening, Collins and some 250 other invited guests form the Hill, NASA, the aerospace industry and the media heard Daniel Boorstin, the Librarian of Congress, ask the question that had been asked of him: "Why, when people in this country seen to have lost interest in space, do we go to the trouble of putting on an exhibition about it?

"If the scientists and politicians don't have the perspective, the Library of Congress has to remind them of the great American adventure," said boorstin. "It's a week of celebration and in it we're going to remind you of the beginning of the beginning."

The "beginning of the beginning" arose in what Leonard C. Bruno of the library, who supervised the exhibit, called "a unique set of circumstances all coming together" - among them Russian cosmonaut Yuri Gagarin going into orbit on April 12, 1961, and five days later the Bay of Pigs.

"The United States was second-best," said Bruno, "and you had a young president, a war hero, looking for worlds to conquer. Prestige-wise, the U.S. was in trouble."

On April 20, 1961, President John Kennedy wrote a memo to the vice president, naming him chairman of the Space Council and asking if there was a chance of beating the Russians by going to the moon or launching any other space program "which promises dramatic results which we could win."

lyndon Johnson's efforts to get the answers brought together a committee of 15, several of whom were at last night's party sponsored by Doubleday to promote their new book on Werner von Braun.

"Lyndon Johnson had some sense of history and wanted the answer to be favorable," remembered Charles S. Sheldon II, now with the library's science policy research division, but in those days a staff member of the original space committee of the House. "Johnson went around the table and, looking directly into our eyes, said to each of us, 'I'm so glad you came.'"

Some people said it was Gagarin who turned the tide, others said it was the Bay of Pigs. But according to Sheldon, the insipiration that "sold everybody, including Jim Webb," came from "a rather milquetoast type": the late Dr. Hugh Dryden, deputy administrator of NASA.

James Webb, whom John Kennedy chose as NASA director, was in last night's crowd, hailed by friends as well as strangers as an administrator par excellence who had known Washington like the back of his hand.

"He played Congress like a violin," said Bruno, who added that he doubted the $20-billion moon program could ever have been completed without Webb.

"The money came because Congress had confidence we would succeed," said Webb, dismissing himself as "just one of the people who worked there."

Now retired, the 72-year-old Webb underwent open-heart surgery last fall. "They did a good job of patching me up," he told Washington attorney Leonard Marks. Current NASA administrator Robert A. Frosch, the only other person with whom Boorstin shared the rostrum last night, said that besides being "an act of human courage, of competition, of engineering and managerial skill, going to the moon was an act of imagination . . . We need to continue with the fantasy and exploration, dreaming which we imagine."

If some saw similarities between Kennedy's bold action in 1961 and President Carter's efforts now to solve the enegry crisis, there were others in the crowd who called it "comparing apples and oranges." CAPTION: Picture, Robert Frosch, Daniel Boorstin and astronaut Michael Collins, by Joe Heiberger - The Washington Post