Yesterday's Washington Post Book and Author Luncheon proved that the main course does not have to come in the middle of the meal.

Although he was the last of three speakers, former budget director David Stockman was clearly the main course. He told a capacity crowd at the Washington Hilton that he was "a first-time author and maybe, as a result of the reaction, a last-time author."

"My book is definitely in the nonfiction category," said Stockman, referring to President Reagan's labeling his "The Triumph of Politics: Why the Reagan Revolution Failed" as "fiction."

Dan Greenburg, who penned "Confessions of a Pregnant Father," was the first speaker introduced by the moderator, Washington Post Managing Editor Leonard Downie Jr. A mostly female audience grimaced as Greenburg recounted his observations of his wife's pregnancy with their first child, namely watching her brassiere size grow as her pregnancy progressed.

"First it was a 32, then it was a 36 triple D, then a 42 . . ." he intoned. One day, he said, he came face to face with the largest brassiere he had yet seen, hanging in the bathroom.

"It was one that I was not comfortable being alone with," said Greenburg.

Greenburg also said his trepidation about fatherhood was really a tussle with the possibility that he "might be afraid to grow up."

Peter Maas talked about his latest true-life thriller, "Manhunt." The book follows the case of Edwin P. Wilson, the CIA agent turned arms and explosives runner, and Larry Barcella, the Justice Department attorney who finally sent Wilson to prison. Maas, who also wrote "Serpico," said America is still paying the price for Wilson's channeling of explosives to Libya. He also attacked what he called the lackadaisical attitude of the various agencies involved with the Wilson case.

"The CIA was aware of it and really did very little . . . it sucked its collective thumb," said Maas.

Then it was Stockman's turn. He began by talking about the burgeoning deficit, playing off Greenburg's tale: "First I saw that it was at $50 billion, then 72, then 150 . . . "

Stockman said he had been criticized for writing that former Reagan aide Michael Deaver, who has lately been criticized for his lucrative consulting business, did not contribute anything of substance to White House policy-making. Deaver's lawyer, Stockman joked, called him to "thank me for the unsolicited testimony."

Stockman told the audience his book gives "credit to the leadership of Congress" for cutting the deficit as much as it has, and for preventing a larger fiscal catastrophe. The problem, explained Stockman, is "I did it in the last chapter . . . some people haven't gotten that far."