In an unusually sharp rebuke, NATO Secretary General Joseph Luns criticized the United States today for allowing the impression to grow in Western Europe that it is reluctant to pursue arms control negotiations and is preoccupied with achieving military supremacy.

In a blunt speech dealing with strains in the Atlantic Alliance, Luns specifically chided the Reagan administration for its recent decision to go ahead with the production and stockpiling of neutron warheads.

"In all frankness," Luns said, the August decision, which was made without consultation with the allies, "was not an example of tact in the conduct of international relations."

Luns made the comments in an address to the North Atlantic Treaty Association in London. The association, a nongovernmental body that seeks to inform the public about alliance issues, opened its 27th annual assembly today.

At the same time that he criticized the Reagan administration, Luns, 70, also took to task West Europeans whose anxieties over the planned deployment of new medium-range nuclear missiles in their countries have, he said, seriously threatened the unity of the North Atlantic Treaty Organization.

Noting that the missiles plan was a European initiative, Luns said that he was "appalled at the way people who know better have allowed the myth to spread that the modernization is an initiative being foisted by the United States upon its European allies."

The Dutchman scolded other West European officials for not making enough of the fact that Moscow spent six months last year ignoring NATO's offer to start arms control negotiations. He also said that "too much emphasis has been placed on the arms control track of the December 1979 decision without giving equal time to the military rationale" for the missiles plan.

But Luns warned that the new U.S. administration "has tended to be too lax in putting its positive interest in effective arms control across to the public" and has "allowed the impression, albeit false, to grow that it is reluctant to pursue the subject and is preoccupied with the pursuit of military supremacy."

This U.S. image, he said, could be harmful to transatlantic harmony. "The Americans should not allow themselves to be seen in Europe as less interested in the opportunities for arms control than the Europeans," he said.

Luns' criticism came one week after a U.S.-Soviet agreement to begin negotiations Nov. 30 in Geneva on limiting the number of European-based nuclear weapons, and one day after a senior U.S. arms control official disclosed in Brussels that U.S.-Soviet talks on limiting strategic weapons would also resume next year.

It also followed a major U.S. bid to focus European public attention on the Soviet threat by the release Tuesday of a report on Soviet military power. But the Pentagon study caused few ripples today in Western Europe and received a generally quiet official European welcome.

The low-key greeting given the booklet by most Western European governments appeared intended to guard against its leading to renewed disputes over U.S. and Soviet military postures in a way that might draw attention away from the renewed moves towards arms control talks.

In West Germany, which is preparing for an official visit in November by Soviet President Leonid Brezhnev, government spokesman Kurt Becker said the Pentagon study had been mentioned at a Cabinet meeting today and he described it as "a contribution to portraying in concrete terms the extent of the threat" from the Soviet Union.

But he noted that the study was "an American report" and told reporters, "There is no question of the federal government of Germany opening a debate on this."

In the Netherlands, where opposition to the planned stationing of U.S. Pershing II and cruise missiles in late 1983 is keenest, the government made no official comment on the report. When asked about the study, Jan Willem Bertens, the Dutch Foreign Ministry spokesman, said his government "always welcomed these kinds of studies."

The strongest official European endorsement came from British Defense Minister John Nott, whose remarks to reporters Tuesday on the importance of the study and the danger of the Soviet threat sounded much like U.S. Defense Secretary Caspar W. Weinberger's.

But the British press did not pay much attention to the Pentagon report or to Nott's comments, and the report was not mentioned in a British Labor Party debate on disarmament this morning.

West German television commentators and some newspapers said the study would have been more helpful if it had compared the Soviet defense effort with Western military strength. There was also criticism that the report had substituted a sketch for an actual photograph of the Soviet SS20 rocket, which the new NATO missiles are intended to offset.

But the West German newspaper Frankfurter Allgemeine applauded the report for at least putting up a counterattack to Soviet propaganda. The paper expressed the hope that the report's contents would be heard by East Europeans listening to shortwave radio.

West European officials declared that the impetus for the U.S. study had come from their own defense ministers after classified briefings by Weinberger in Brussels and Bonn last spring about Soviet conventional and nuclear capabilities. A number of the ministers requested then that the information be declassified and made public to help dampen opposition to NATO nuclear modernization plans.

In his speech, Luns accused West European governments of not firmly supporting the NATO missiles modernization plans.

"As a European myself," he said, "I can readily sympathize with the anxieties that the issue of theater nuclear force modernization has aroused on this side of the Atlantic.

"What I am unable to sympathize with, however," he continued, "are the defensive, almost apologetic tactics many allied governments have adopted in treating those anxieties.

"These tactics have in my view mainly served to ensure that the issue, which was bound to be difficult enough anyway, would become a major threat to transatlantic unity, which it has," Luns said.

Washington Post correspondent Leonard Downie Jr. contributed to this report from London.