NATO foreign ministers, seeking to minimize differences that blocked an alliance endorsement of research on President Reagan's Strategic Defense Initiative, declared their support today for "U.S. efforts in all three areas" of the Geneva arms talks with the Soviet Union.

By putting that language in the communique ending the meeting here of the North Atlantic Treaty Organization, the ministers enabled Secretary of State George P. Shultz to say that the 16-nation alliance remains united behind all aspects of America's Geneva negotiating posture, including SDI or "Star Wars."

The Geneva talks involve intercontinental nuclear missiles, medium-range missiles and missile defense systems based in space. The Soviets have sought to link cuts in offensive missiles to U.S. abandonment of SDI research.

Shultz had sought to counter impressions that SDI has become a divisive issue within the alliance by a formal endorsement in the communique. But his hopes were blocked by France, which is deeply mistrustful of Reagan's emphasis on Star Wars technology and which had threatened to dissociate itself from an endorsement.

Shultz acknowledged at a news conference that the United States would have liked explicit language in the communique, but he added:

"We take great encouragement from the very strong endorsement of our negotiating effort in Geneva in all three of the negotiating groups . . . It would be a great mistake if anyone were to think that the research program of the United States is in any way deflected. It would be a great mistake to take from this the view that there is anything but widespread support from our allies on doing this research."

Similar statements seeking to play down the disputes over SDI were made by British Foreign Secretary Geoffrey Howe, West German Foreign Minister Hans-Dietrich Genscher and the NATO secretary general, Lord Carrington. Carrington said:

"We didn't have a row. I recognize that not every government would agree with every detail. But I believe the idea of American research being prudent in view of the fact that the Soviets are doing similar research is pretty near the center of gravity within the alliance."

In addition to the differences over SDI, the meeting saw the European members unanimously stress to Shultz their desire for the United States to continue abiding by provisions of the unratified SALT II arms control agreement.

In what was widely taken as a hint that the administration will adopt a compromise position adhering to the spirit if not the strict letter of SALT II restraints, Shultz stressed that "we value the opinion of our allies, and the views that they express to us are taken into account."

Today's communique also reaffirmed NATO's willingness to halt or modify deployment in Western Europe of U.S.-made intermediate-range missiles if the Geneva talks produce an agreement on reduction or elimination of such weapons.

The ministers also agreed that NATO should be represented "at ministerial level" when the 10th anniversary of the Conference on Security and Cooperation in Europe is celebrated in Helsinki in July.

Shultz, acknowledging that he will go to Helsinki, said he expects to confer there with Soviet Foreign Minister Andrei Gromyko.