President Reagan will deliver the first major foreign policy speech of his presidency Wednesday, on reducing the threat of limited nuclear war in Europe.

Reagan will speak in the wake of mounting fears triggered by his and his advisers' impromptu comments on the possible use of atomic weapons in Europe.

White House officials said that the speech, which they are calling a "major address," has been "under consideration for a while." It is scheduled for 10 a.m., at the National Press Club.

Reagan is expected to announce that the U.S. goal in upcoming European theater weapons negotiations will be to reduce to zero all intermediate- and medium-range nuclear missiles in the hands of North Atlantic Treaty Organization and Warsaw Pact forces.

This U.S. position, which sources said was approved in the last few days, expands the so-called "zero option" originated by European allies led by German Chancellor Helmut Schmidt.

The decision to deliver the speech Wednesday was made just this week, however, as presidential advisers apparently were anxious to generate major substantive news after the president was buffeted by the controversies, not of his doing, involving Office of Management and Budget Director David A. Stockman and national security adviser Richard V. Allen.

Presidential advisers concluded that the National Press Club was the best available forum for such a speech. But they then found themselves in the position of having to settle for the unusual mid-morning timing in order to assure that Reagan would be able to make the speech on the earliest possible date. The president of Venezuela, Luis Herrera Campins, was already scheduled there for noon the same day.

For today, the president's advisers also added a tour of the Pentagon to Reagan's schedule, which will provide an opportunity for evening television coverage of his demonstrated concern for national security.

Reagan came under sharp criticism in Europe recently after he remarked to a group of editors, in answer to a hypothetical question, that "I could see where you could have the exchange of tactical weapons against troops in the field without it bringing either one of the major powers to pushing the button."

The statement was consistent with longstanding NATO understandings, but it touched off a wave of criticism in Europe, where there are fears that the continent may become the battleground for a U.S.-Soviet nuclear clash.

Those fears were heightened when Secretary of State Alexander M. Haig Jr. and Defense Secretary Caspar W. Weinberger got themselves into a very public disagreement over the nuclear policy in Europe. First, Haig testified on Capitol Hill that for years NATO has had a contingency plan permitting detonation of a demonstration nuclear weapon in an unpopulated area in the event of Soviet attack to warn that nuclear weapons could be used.

The next day, Weinberger testified that there was no such plan. And the matter was further muddled last week when Reagan told a news conference he had received no answer as to which of his advisers was correct--which forced White House aides to say that the president really did have the answer, but he just didn't want to say it.

Yesterday, NATO Secretary General Josef Luns, conferring here with Haig and other U.S. officials, said that the anti-nuclear protest in Europe is more than just "a fringe of left-wing, rather young people."