Ronald Reagan believes Mikhail Gorbachev is a different kind of man from his Soviet predecessors, and this belief enables our president to set aside a lifetime of caution concerning what communists are like and how we should deal with them.

The president is not alone in his view. Underlying the euphoria of the summit week was a widespread notion that Gorbachev is a new kind of Soviet ruler, with new goals for his country and new views about how to achieve them. This optimistic belief is based not only on our national character, but also on Gorbachev's style and on the fact that he represents a new generation of Soviet leadership.

The style is that of a modern man. Gorbachev does not sound like a man who threatens anyone's security. So many of his Western hearers, including the American president, conclude that the country he rules is less aggressive and expansionist than in the past. Months ago, George Shultz argued that Gorbachev was a new type of Soviet ruler. Reagan then resisted this view. Now he believes it.

The belief is not implausible. We regularly assume that style is an external reflection of internal realities, and as far back as Plato, discerning people have believed that political generations sometimes differ in fundamental ways, that the arrival of a new generation in power may mark the beginning of a new political era.

Moreover, we Americans have wanted desperately to believe in a transformation of the Soviet Union and of U.S.-Soviet relations. Most Americans have, therefore, been enormously gratified and encouraged to hear of Gorbachev's campaign for ''glasnost'' and ''perestroika'' and ''new thinking.''

People rethinking their view of the Soviet Union, including Ronald Reagan, would be well advised to actually read Gorbachev's new book -- dull as it is -- which casts great light on his conceptions of where the Soviet Union is, where it is going and why. The Gorbachev who wrote "Perestroika" is a classical Leninist -- flexible, adaptable, skillful in the pursuit and use of power, absolutely committed to ''the revolution,'' to socialism, to a one-party state, and not unduly disturbed about the high human cost of past Soviet policy.

The book rejects utterly the common American view that economic difficulties have prompted Gorbachev's campaign of reform, and that these reforms constitute a retreat from socialism. Again and again, Gorbachev insists that his goal is the consolidation and perfection of socialism, not its modification.

''We will proceed toward better socialism rather than away from it,'' he writes. ''We are saying this honestly and without trying to fool our own people or the world. Any hopes that we begin to build a different, non-socialist society and go over to the other camp are unrealistic and futile.''

Concerning democratization, he says it is indeed a goal. But, as he has emphasized in Moscow conversations and makes clear in the book, the democracy he seeks is not American-style, Western-style democracy in which rulers are chosen in periodic, competitive elections under conditions of free press and assembly. The democracy Gorbachev seeks means decentralization and broad participation in society. It does not and could not mean competitive elections, for, as Gorbachev remarks without embarrassment, ''We have no political opposition.'' The party rules.

If perestroika is not a retreat from socialism and not a drive for liberalization caused by Western pressures, then what is it?

''It is a revolution. A decisive acceleration of the socioeconomic and cultural development of Soviet society which involves radical changes.. . . It is a jump forward in the development of socialism . . .'' he writes.

There are few surprises in this book. From it we learn that Gorbachev is a Soviet national who clings firmly to Leninism and the one-party state. We also learn that his foreign-policy approaches are the same as would have been assumed by any close observer.

There are the familiar justifications. The Soviet Union went into Afghanistan ''because its leaders asked the Soviet Union to help.'' There is no mention here of the murders of those same Afghan leaders at the hands of their Soviet ''benefactors'' within hours of the Soviet Army's arrival. There is the familiar theme that ''Europe is our common home,'' a Europe that ''stretches from the Atlantic to the Urals.'' Russians then are European. Americans are not. Russians seek to realize closer bonds with their ''common family.''

There are harsh, familiar complaints about America's role in the world. U.S. foreign policy is depicted as being dominated by a ''cave-man'' mentality that sees the Soviet Union as a persistent threat to the world. ''We have the impression that the United States needs regional conflicts to maintain its confrontation with the Soviet Union,'' Gorbachev says.

''What motivates the United States?'' Gorbachev asks and answers. The old villain, the military-industrial complex. American foreign policy is based on illusions of technological superiority and the belief that ''the economic system of the Soviet Union is about to crumble,'' that it will be possible to restore American military supremacy.

America is not the only target. Gorbachev reaffirms Soviet opposition to ''any manifestations of nationalist narrow-mindedness and chauvinism, parochialism, Zionism and anti-Semitism in whatever forms they may be expressed.''

His conception of the Soviet past is conventional, orthodox and unembarrassed. He describes the collectivization policy that killed 5 million people as ''a great historic act, the most important social change since 1917.''

The book lacks the charm and flexibility that characterize Gorbachev himself. It is dull; he is not. Perhaps he did not write the book at all. Gorbachev describes perestroika as a revolution. But the book testifies that Gorbachev is no revolutionary within the Soviet tradition. I hope the president reads it before the next summit.