We are told by many commentators that the Geneva summit, for all of its cheerful atmospherics, produced nothing of value in U.S.-Soviet relations that can be measured, weighed or codified.

We are told that summits are historically worthless, that the Soviets are deploying unverifiable mobile missiles and that President Reagan is undeterred in his plans to build what the Soviets consider a threatening missile defense. We are told that nothing has changed and that the arms race will continue until Armageddon.

This conventional wisdom may be correct. But as a journalist who has spent two decades observing Reagan and trying to understand how he responds to events, I tend to think that the Geneva summit may be one of the best things that ever happened to him.

It is a good thing because Reagan, among the least analytical and most unread of presidents, learns deeply from personal experience. When aides in California wanted to save a wild river, they exposed Reagan, who was then governor, to its beauty. When White House advisers wanted to change Reagan's perceptions about China, which he used to think was synonymous with Taiwan, they arranged a state visit to the People's Republic of China from which he emerged with favorable views.

In short, Reagan is not a briefing-book president. He learns by doing, and the language he uses to describe his experiences is critically important. After Reagan visited China, it became "so-called Communist China," a pardonable exaggeration that reflected the change that had occurred in the president's mind.

Reagan had no such right-handed praise for the Soviets after Geneva, nor do they deserve it. But he spoke proudly of "improving our relationship," a goal that was alien to him when he took office and that some supporters still consider a dangerous delusion.

What the president chose not to say also was important. Reagan used to call communists liars and cheats and say the Soviet Union was the "focus of evil" on this planet. This view was reflected in administration policies and its unremitting hostility to the Soviets.

Reagan also understands the importance of language when employed against his policies. In Geneva, at one of those interminable "photo opportunities," Reagan was asked how Gorbachev could "help" in dealing with the U.S. Strategic Defense Initiative. "Well, first by stopping calling it 'Star Wars' and calling it what it is -- a defensive shield, instead of an offensive weapon," Reagan replied.

Gorbachev has not altered his view about Reagan's missile-defense plan, which he believes is the dangerous path to offensive weapons in space. But in his post-summit news conference, the Soviet leader called the project "SDI," not "Star Wars," which is a start toward international truth in labeling. Gorbachev, who said both nations must learn "the art of living together," declared that he and Reagan no longer indulged in the "stupid" practice of name-calling.

Apart from breaching the rhetoric barrier, Reagan and Gorbachev made a useful contribution simply by getting to know each other in private and intense discussions. It has become a cliche to say that we live under a nuclear cloud and that the superpowers have the military capability to produce a world in which the survivors would envy the dead. The idea is so numbing that most of us put it out of our conscious thoughts even though we realize that miscalculation or accident could someday trigger a nuclear catastrophe.

In this kind of world, it is self-evident that the leaders of the superpowers ought to understand each other's hopes and fears, if only to provide what my colleague Don Oberdorfer has called a "fail-safe for humanity" in times of crisis. Saying this does not mean that we and the Soviets "are alike" or that we should disarm or that the arms race will be curbed by the cooing at Geneva.

What it does suggest is that resumption of personal relationships between U.S. and Soviet leaders was long overdue and may be especially important for Reagan. For a president whose touchstone is experience, this relationship is bound to contribute to his understanding. What is good for Reagan, in this instance, should also be reassuring for the world.

Reaganism of the Week: Explaining to Congress Thursday his effort to improve U.S.-Soviet relations, Reagan said: "No one ever said it would be easy. But we've come a long way."