Ronald Reagan claimed in his autobiography of 20 years ago that he had "missed a lot of career opportunities" because of "mental absorption" with the activities of the Screen Actors Guild, of which he was president for six years and which he led in its first successful strike.

What Reagan had in mind was his acting career. But since then, nothing has served him better as governor of California and president of the United States than the experience gained at the bargaining table in Hollywood.

Once past the shaky novitiate of his governorship, Reagan has followed a fairly consistent pattern on issues that matter most to him. Typically, he stakes out a firm opening position, refuses to make concessions in advance, holds his bargaining cards close to his vest and strikes a compromise only when in danger of losing a negotiation.

In 1983, for instance, Reagan proclaimed that 10 percent real growth in the following year's defense budget was the "absolute minimum" necessary to keep America strong. When a compromise of 7 percent was produced, he said it "shortchanges the nation's security." Eventually, he settled for just under 4 percent, on which the Defense Department has done quite nicely.

Reagan's strategy of asking for a lot and settling for reality has prevailed on other big-ticket domestic items and seems to have crept into his dealings with the Soviets. It is an article of faith with him that an agreement always differs from either side's initial offer.

In 1980, Reagan campaigned for increased military spending but refused to be pinned down to a number. After his election he upped the ante beyond the 6 percent growth he had been expected to seek, saying that defense deficiencies were worse than he had known. His standard line, well into his presidency, was that "you do what's necessary for national security and then add up how much it's going to cost."

Now there is a variation on the theme. In budget talks with the Senate, Reagan contends that defense cuts must not touch "vital weapons systems, either conventional or strategic." This sidesteps the question of which systems are vital but leaves Reagan running room with Congress.

In assessing Reagan's performance beyond his public-speaking role, it is often difficult to know the depth of his knowledge, understanding and involvement. Martin Gottlieb of the Dayton Daily News has dubbed the president "the Inspector Clouseau of politics," after the hero of the Pink Panther movies, whose charm was "that he succeeded brilliantly and consistently even though he didn't have a clue in the world about what was going on."

Maybe so. Certainly, Reagan seems to have blundered through in Clouseau-fashion on the MX missile, about which he knew so little that he scrapped a well-conceived plan of President Jimmy Carter's and wound up supporting the basing of the controversial missile in highly vulnerable old silos.

Reagan is light-years ahead of Carter and many other presidents, however, in the way he focuses arguments and political assets to win his way with Congress. He keeps winning as his advisers keep changing, which suggests that Reagan must have something to do with his success.

In the latest round of budget bargaining, the old Reagan formulation of doing "what's necessary" has prevailed. By emphasizing weapons systems rather than growth percentages, the administration has forced Congress to concentrate on difficult choices when its leaders would have preferred to throw numbers back at the White House.

"That is the way the president's mind works," says a longtime aide. "He has created the conditions for a face-saving compromise in which he can take credit for saving systems and Congress can take credit for cutting the defense budget."

A compromise that gives everyone something to crow about is the essence of success in any negotiation. Despite the hard edge to recent presidential speeches and the confrontational approach of his latest team, Reagan remains a political realist. Scratch the Great Communicator and one finds a pretty good negotiator inside. Reaganism of the Week:

At a breakfast with reporters last Monday, Reagan was asked whether he wished he hadn't joked at the Gridiron Dinner the previous Saturday: "I think we should keep the grain and export the farmers." "Yes," he replied, "because it didn't get a laugh. But I thought that Gridiron was supposed to be off the record . . . . I think if that isn't true, why, it's going to kind of curb the humor at the forthcoming Gridirons."