For conservatives, Ronald Reagan's foreign policy has produced much surprise but little delight. His fourth and, one prays, final summit is a suitable occasion for conservatives to look back with bewilderment and ahead with trepidation.

It is true, as some Europeans argue, that conditions are better in Europe, the region that remains the decisive prize in the East-West contest. Just 15 years ago there still were two dictatorships in Western Europe (both in the Iberian peninsula), terrorists seemed able to destabilize Italy and perhaps West Germany, and ''Eurocommunism'' seemed the wave of the future. Today the dictatorships are gone, terrorists cannot be decisive anywhere, and communist parties are withering away. But Reagan administration policies had little to do with any of this.

Furthermore, it is arguable that Reagan will leave U.S. security as precarious as it was in 1980. This is so for three reasons:

First, his deficits, combined with his success in making low taxes the crux of contemporary conservatism, have put in place a decade -- at least -- of pressure against defense spending. That pressure already has pushed defense spending into decline, in real terms, since 1985.

Second, Reagan's rhetoric has accelerated the nation's intellectual disarmament. In his seventh and eighth years, he has declared the Cold War over. He has done this by declaring that the Soviet regime had been readily transformed for the better by the sudden, inexplicable capture of it by a man (Mikhail Gorbachev) who supposedly is opposed to its 70-year-old expansionist tendency and rationale. That statement was bad enough.

But worse was Reagan's statement that the Soviet regime's inherent tendencies were not radically wrong until the regime was hijacked by Stalin. Stalin, said Reagan, was not, as conservatives believe, an intensification of Lenin, but was merely an aberration.

Third, by succumbing so fully to the arms control chimera, Reagan made it impossible to conduct a coherent conservative foreign policy. Indeed, a case can be made for the proposition that, thinking only of U.S.-Soviet relations, a Dukakis presidency might be preferable to a Bush presidency of more Reaganism.

To allay foreign and domestic doubts about a Democratic president, and because he favors enhanced conventional forces, which are expensive, President Dukakis might propose a modest -- say, 2 percent -- increase in defense. George Bush might also. But a Democratic Congress, which is a certainty, would give a Democratic president his defense budget. It would cut Bush's.

Furthermore, when there is a Democratic president, it is possible to have cohesive conservative opposition to at least some arms control excesses. When a Republican is president, such opposition is impossible. The Soviet invasion of Afghanistan may have been President Carter's pretext for withdrawing SALT II from Senate consideration. However, a sufficient reason for withdrawal was a block of at least 34 votes against it, enough to defeat it. A Democratic president was a necessary condition for such opposition, which is almost entirely Republican.

There is no reason to doubt that Bush would be as ready as Michael Dukakis is, or as ready as Reagan has been, to make arms control agreements the controlling aspiration of U.S. policy. That aspiration makes a coherent conservative foreign policy impossible, for reasons explained in Commentary magazine by Mary Eberstadt, a member of the State Department Policy Planning Staff between 1985 and 1987.

Consider, she says, the collapse of administration policy regarding Nicaragua. By 1987, the administration clearly was ready to make arms control the altar on which anything else would be sacrificed. By summer 1987, the contras were a sacrifice.

The argument for contra aid was grounded in an ominous interpretation of Soviet intentions in the world. By the end of 1987, the administration had abandoned the interpretation (had it ever been more than rote even to Reagan?) of the Soviet Union as possessing dangerous hegemonic aspirations.

Absent a connection with such aspirations, it does not matter all that much if there are, as Secretary of State Shultz has warned that there will be, ''two, three, many Nicaraguas.'' Administration rhetoric about the peril of an unchecked Nicaragua was refuted by administration rhetoric about the new, transforming Soviet leadership that the administration assures us is searching for accommodation, as demonstrated in the arms control ''process.''

Either the arms control fixation or the contras had to go. The contras are gone. Noriega is not. These facts testify to the impotence, bred by incoherence, of Reagan's foreign policy.