Like generals who learn the lessons of past wars, President Reagan's advisers may have drawn upon the wrong experience in preparing him for this week's meetings with Soviet leader Mikhail Gorbachev.

These advisers believe that Reagan should not be stuffed like a sausage with facts and statistics, as he was for his first debate with Walter F. Mondale. Struggling to incorporate the voluminous information provided by his aides into the points he wanted to make, Reagan became so inarticulate that he raised doubts about his competence. Left relatively alone for his rematch with Mondale, the president made effective use of one-liners, subdued the competence issue and went on to a landslide victory.

But Reagan is on a different stage in Geneva. This time, he will be tested at close range in private discussions where the 54-year-old Gorbachev will seek to evaluate the grasp and intentions of Reagan, who is 74 and has three years left in his presidency. If Reagan casually entertains the idea of a "nuclear-free zone" in Europe in contravention of NATO doctrine or gives goofy explanations of missile defense, as he has done in recent interviews, it will not easily be corrected by a revisionist explanation from White House spokesman Larry Speakes.

That is one of the dangers of this summit, although probably not an apocalyptic one. The Soviets can be patient when it suits their purposes, and they are not troubled by the democratic inconvenience of elections. If Gorbachev finds Reagan deficient in understanding vital complexities, he has the alternative of waiting for the next president.

That might be okay for the Soviets, who no doubt will pursue their own missile-defense system while waging a propaganda campaign against Reagan's Strategic Defense Initiative. But a stumbling presidential performance at the summit could dismay Capitol Hill and undermine Reagan's attempts to pry money from Congress to keep the U.S. program alive.

If recent interviews are a guide, Reagan doesn't know very much about weapons systems, missile defense or history. The president's men might have been well advised to face this reality, put aside the Mondale experience and take the risk of "overpreparing" Reagan for his important meetings with Gorbachev.

Admittedly, this is more easily said than done in dealing with a president never menaced by the strain of intellectual overwork. Ever since California Gov. Reagan confessed at a 1967 news conference that he could not identify a single item of his legislative program, his advisers have been struggling to find an effective formula for preparing him.

"We've declared a cease-fire in the battle for Reagan's mind," Edwin Meese III said during the 1980 presidential campaign, relieving a tense moment with a quip that showed insight into Reagan's lack of understanding and the divergent counsel of his advisers.

The conflicts among the advisers, even deeper on arms control than they were on campaign strategy, are centrally related to Reagan's fundamental lack of knowledge. When a chief executive cannot discuss the substance of complex policy issues, it is inevitable that subordinates will make their own judgments and seek to gain the president's ratification of them. This has happened on arms control throughout the Reagan presidency. It is still happening.

All that said, it is also true that Reagan has the support of a majority of Americans and two attributes that have served him well in tight spots. The first is a compelling personality to which even Gorbachev may not prove immune. The Soviets should leave the summit convinced that Reagan will go back to Congress for more defense spending if there is no progress on arms control. Reagan also has a penchant for rising to the occasion in critical situations. He is, in sports terms, a big-game player.

Secure in this knowledge, Reagan's advisers have prepared him for the competition of Geneva with films and conversations that have, in easily digestible bits, ostensibly brought him up to speed about the Soviet Union. It is devoutly hoped that Reagan is as ready as his managers believe.

Reaganism of the Week: Explaining the Strategic Defense Initiative to European broadcasters Tuesday, the president said: "But we will make available to everyone this weapon. I don't mean we'll give it to them. They're going to have to pay for it at cost."