Despite budget negotiations on the Hill that took President Reagan and top White House officials to the Capitol, the Hoover Institution drew a sizable representation of top administration officials for its reception last night in honor of its public affairs fellows.

Among them were Attorney General William French Smith, Federal Reserve Chairman Paul A. Volcker, United Nations Ambassador Jeane Kirkpatrick, FBI chief William Webster and Assistant Attorney General William F. Baxter, head of the Justice Department's antitrust division.

"I stay as far away from economics as I can," the attorney general replied after the observation that he made it to the late-afternoon reception at the Sheraton-Carlton.

The turnout from the administration was not surprising. It had the flavor of a class reunion of past and present graduates. The Hoover Institution at Stanford University has supplied the Reaganites with many of their people and ideas. Glenn Campbell, its director, served on a personnel search committee when the president-elect was seeking advice on appointments. Smith was also on the committee.

Volcker showed up toward the end of the reception. He said he had heard that the news of the budget talks on the Hill wasn't "that optimistic--just the opposite."

More than 400 guests attended the reception to honor the West Coast think tank's public affairs fellows, who come to Washington to work with congressmen or administrative agencies. The institution also has national fellows, drawn from the academic community.

John Cogan, who was a 1979-80 national fellow, now is assistant secretary of labor for policy evaluation and research.

"As an academic, I was able to sit back and think quietly about a problem before making a decision," Cogan said. "Now decisions have to be made immediately on scanty evidence. But that's the way the world works."

There was Cogan, the former professor at Stanford, being congratulated that one speech of his (on unemployment) has been printed in "Vital Speeches of the Day," a private publication that rounds up important government speeches.

Richard Allen, Reagan's former national security adviser, said he is keeping busy on his four jobs: a counselor to the Republican National Committee, a director of the Heritage Foundation, a private consultant and a speaker on the lecture circuit. Without the pressure of public office, he says, he is following an aerobics routine: "I do either 10 miles on a bike or 100 lengths in the swimming pool--1 1/2 miles--at least three times a week."

The reception also drew some names from the conservative past. There from the Nixon administration was Melvin Laird, former secretary of defense and now with Reader's Digest magazine, and Pat Buchanan, former White House speechwriter, who now writes a syndicated newspaper column and appears as a television and radio commentator.