The Soviet Union reacted to President Reagan's European tour with exceptionally sharp criticism today, accusing Reagan of rejecting the principle of peaceful coexistence and dreaming of going down in history as "the gravedigger of the ideas of detente."

This harsh reaction followed a week of ambivalence by the official Soviet media in covering Reagan's just-concluded trip. Reagan's tactic of coupling searing words on the Western quest for freedom with offers to Moscow of steps to reduce the dangers of war apparently confounded Soviet officials. The media carefully paraphrased Reagan's pronouncements; not once was he quoted directly.

The acrimonious commentaries--one a signed article in Pravda that reflected highest level Kremlin authorship--indicate that Moscow no longer sees Reagan as a simplistic cowboy shooting from the hip with ill-conceived statements. Instead, he now appears to be seen here as a far more dangerous politician out to inflict maximum damage on the Soviets in the propaganda battle for Western European public opinion.

Earlier, the president's musings about the possibility of limited nuclear war and other off-the-cuff remarks had led Western diplomats here to joke that perhaps the president and his secretary of defense were covertly working as consultants for the Kremlin's propaganda bureau.

But Reagan's speeches during his tour of Western Europe obviously had been tailored skillfully, it is felt here. His emphatic call in London for an anticommunist crusade was carefully balanced, in a speech in West Berlin, with offers of steps designed to build mutual confidence. These included a proposal to exchange more information on missile tests and on the capabilities of strategic weapons, but they were not published here.

Reagan's adoption of a more moderate stance actually had started before his European trip when he offered to meet Soviet President Leonid Brezhnev and then called for a sharp reduction in nuclear arsenals of the two countries to be negotiated at the forthcoming strategic talks in Geneva. He also promised to abide by the provisions of the second agreement reached at the strategic arms limitation talks, an accord he previously had described as being "fatally flawed."

The Soviets were skeptical about Reagan's conversion, arguing that it was designed to take the steam out of the antinuclear movement in Western Europe and the United States. Yet the fact that the president seemed to have embraced more moderate positions has led some Soviet analysts to voice hopes that a constructive dialogue with the Reagan administration may be possible after all.

Now, Reagan's tour of Western Europe appears to have heightened Soviet skepticism again.

The Pravda commentary charged that Reagan's foreign policy "is the main source of current world tensions" and that this was demonstrated by his speeches in London and Bonn.

The government news agency Tass commented that the speeches showed Reagan was "obsessed by truly boundless, imperial ambitions" and that he "not only rejects the principle of peaceful coexistence but also, judging by everything, dreams of going down in history as the gravedigger of the ideas of detente."

The president's "belligerent rhetoric," Tass said, "revives the atmosphere of the worst times of the cold war."

It continued, "The president's London speech has further bared the aggressive, hegemonistic essence of the extremely dangerous foreign policy course that is being pursued by the present Washington administration and determined the ideological, propaganda and political content of this course."

The commentary dismissed Reagan's "so-called initiatives" in the area of arms control "whether these concern the lowering of the level of nuclear confrontation in Europe, the reduction of strategic arms or t reduction of conventional armed forces on European soil."

These proposals, the commentary said without giving details of Reagan's initiatives, are "not designed to genuinely curb the arms race" but are "attempts under the peace-loving guise, to secure military superiority for the United States and so that, on acquiring a sword--the longer and sharper the better--they can dictate their will to sovereign countries and peoples."

The commentaries implicitly acknowledge that Reagan has tactically played his hand skillfully. The principal thrust of all commentaries appeared to be aimed at Western Europe with the argument that Reagan's policy was not contributing to a more secure peace in Europe.

The Soviet commentaries also assailed the president personally, describing his speeches as "pompous" and his professions of peaceful intentions as "really blasphemous."