Secretary of State George P. Shultz told the Senate Foreign Relations Committee yesterday that the United States dramatically has improved its overall strength relative to the Soviet Union's in the past four years, paving the way for possible achievements in arms control and U.S.-Soviet relations across-the-board.

In the first of a series of hearings intended to be a "comprehensive review" of U.S. foreign policy, Shultz portrayed the United States and the West as a whole as increasingly strong militarily, economically and politically, while the Soviets face imposing difficulties.

A decade ago, the Soviets "had reason for confidence that what they call the global 'correlation of forces' was shifting in their favor," Shultz said. But today, he declared, "we have reason to be confident that the 'correlation of forces' is shifting back in our favor."

Secretary of Defense Caspar W. Weinberger, the second witness, took a notably darker view. He depicted the Soviets as "building on" a numerical military superiority, "dramatically improving" the quality of their weaponry, continuing to "widen their conventional advantage in nearly every force category" and "expanding the geographical reach" of their forces.

None of the senators on the panel, holding its first day of high-profile hearings under the new chairmanship of Sen. Richard G. Lugar (R-Ind.), said or asked about the divergence of the two outlooks.

Weinberger expressed strong opposition to proposed cuts in the military budget request that President Reagan will send to Congress on Monday.

And he refused under heavy questioning from Sen. John Glenn (D-Ohio) to retract a Defense Department statement, issued in his name last Friday, saying that those who work for success in defense reductions "really mean success in weakening the security of the country."

Glenn demanded that Weinberger apologize for "challenging the loyalty" of critics, especially to the immediate target of Friday's blast, Senate Majority Leader Robert J. Dole (R-Kan.).

Weinberger said he did not harbor "the slightest suggestion of evil motives" in proponents of military cuts. However, he would neither apologize for nor take back the statement made by his press spokesman, Michael I. Burch, and blamed reporters for not checking Burch's remarks with him before publishing them.

Lugar, in a statement that won praise from Democrats and fellow Republicans, opened the hearings by saying that the time is "long overdue" to reexamine the bases of U.S. actions in the world because of major changes and strains in the postwar policy of "containment."

Lugar referred to the growth of Soviet military power since the 1960s and the shattering of American political consensus about foreign policy due to the Vietnam experience.

Lugar paid special attention to Central America in his opening statement and his questioning of Shultz and Weinberger, saying that "scarcely has any foreign policy issue come before the Congress in recent years over which opinion has been more divided."

He added that the nation seems unprepared to deploy U.S. forces directly in the area, to support the program of "covert assistance" to anti-government rebels in Nicaragua or to accept the actions of the Nicaraguan regime. "We simply must overcome our divisions on this issue in the Congress if we are to assist in the development of peaceful and fundamental change in Nicaragua," Lugar said.

Shultz, in a lengthy prepared statement that took about an hour to read, seemed to approve a broad charter for covert U.S. actions against the Soviets in various parts of the world.

"Experience shows we cannot deter or undo Soviet geopolitical encroachments except by helping, in one way or another, those resisting directly on the ground," he said.

Later Shultz remarked that "Marxist-Leninist rulers have found that the aspiration for representative government is not so easy to suppress" in Nicaragua, Afghanistan, Cambodia, Ethiopia and elsewhere in Africa.

He added in the next breath that "Americans have a long and honorable tradition of supporting the struggle of other peoples for freedom, democracy, independence and liberation from tyranny."

The committee's ranking Democrat, Sen. Claiborne Pell (R.I.), charged that the United States has been "supporting terrorists" by aiding the "contra" rebels in Nicaragua, with the result that "several thousand" people have been killed and property destroyed. "One country's terrorist is another country's freedom fighter," Pell said.

"I don't accept that at all," Shultz replied. He said the "contras" are "trying to make a mark" on the Nicaraguan government and "fighting for freedom."

Later, controversy arose about the responsibility for the recent suspension of diplomatic talks between the United States and Nicaragua. Lugar quoted Shultz as saying that "for the moment, Nicaragua does not want to proceed" with the talks and "has contempt for the Contadora process" of regional negotiations.

By this time, Shultz had left Capitol Hill and Weinberger was before the committee. The defense secretary said he understood that "the whole approach and attitude of the Nicaraguans at the final meeting with the United States indicated no reason to continue the negotiations."

He denied reports of a difference of opinion in the administration about breaking off the discussions for the time being, saying it was "a general consensus" to take this action.

Sen. Edward Zorinsky (D-Neb.) quoted Carlos Tunnermann, the Nicaraguan ambassador to the United States, as saying that Nicaragua "pleaded to continue the negotiations" but was turned down.

A State Department official said later that the bilateral negotiations were suspended by Washington because of Nicaragua's unwillingness to work constructively with the Contadora countries on the regional settlement the United States is seeking to advance.

Shultz declined to say what ideas he is considering to resurrect congressional support for aid to the rebels in Nicaragua or to create other pressures against the government.

Shultz's discussion of the Soviet Union included an unusual public tribute to "my able interlocutor, Andrei Gromyko," the Soviet foreign minister, whom Shultz met in arms discussions Jan. 7-8 in Geneva. Shultz called Gromyko "the living embodiment of some of the Soviet Union's great advantages -- continuity, patience, the ability to fashion a long-term strategy and to stick to it."

"The democracies, in contrast, have long had difficulty maintaining the same consistency, coherence, discipline and sense of strategy. . . . Our ways of thinking have tended too often to focus either on increasing our strength or on pursuing negotiations" rather than take "clearly the most sensible course" of doing both simultaneously, Shultz said.

Toting up the score for East and West, Shultz said that "in the last four years, the underlying conditions that affect U.S.-Soviet relations have changed dramatically."

"A decade or so ago, when the United States was beset by economic difficulties, neglecting its defenses and hesitant about its role of leadership, the Soviets exploited these conditions. They continued their relentless military buildup; they and their clients moved more boldly in the geopolitical arena, intervening in such places as Angola, Cambodia, Ethiopia and Afghanistan, believing that the West was incapable of resisting . . . .

"Today the West is more united than ever before. The United States is restoring its military strength and economic vigor and has regained its self-assurance. We have a president with a fresh mandate from the people for an active role of leadership.

"The Soviets, in contrast, face profound structural economic difficulties, a continuing succession problem and restless allies; its diplomacy and its clients are on the defensive in many parts of the world."

Both Shultz and Weinberger spoke in advocacy of Reagan's Strategic Defense Initiative or "Star Wars" plan.

The language of their statements about the use of U.S. force abroad, including U.S. military responses to terrorism, was muted on both sides in a way that deemphasized their past public disagreements.