President Reagan ignored the hard-hitting foreign policy themes of his first two years in his State of the Union address last night and spoke in bipartisan, mainstream terms that could have been used by any of his predecessors in the postwar era.

Although one of his senior White House advisers dismissed the foreign policy and defense portion of the speech as "nothing new" and reflecting "no changes," both the tone and substance of Reagan's pronouncements were startlingly different from last year's State of the Union address and many of the other policy statements of his first two years in office.

Gone were "the Soviet regime," "the Soviet empire," "the shadow of Soviet power" and other such anti-Soviet phrases of the past. Gone was his 1982 State of the Union pledge, in the aftermath of martial law in Poland, that "America will not conduct 'business as usual' with the forces of oppression."

Nowhere to be found in this new world of peace aborning were the "radical forces which threaten our friends," or the Cubans and Libyans "who would export terrorism and subversion in the Caribbean and elsewhere."

Instead, Reagan last night sketched a world whose chief problems are economic, requiring greater U.S. contributions to the International Monetary Fund, and a world of peacemaking American diplomats industriously seeking "constructive negotiation with potential adversaries" around the globe to the applause of a bipartisan cheering section at home.

Regarding the Soviet Union, Reagan emphasized that "we are prepared for a positive change in Soviet-American relations," and expressed his willingness "to carefully explore serious Soviet proposals" on arms control in order to prevent "a wasteful arms race."

He defended U.S. bargaining positions in the Geneva disarmament talks on medium-range and strategic nuclear weapons, and said, "We insist on an equal balance of forces."

In substance, he continued to back a military buildup as a leading task of his administration. But the rhetorical justification shifted from that of negotiating "from a position of strength" (last January) to maintaining "adequate deterrence" (last night). There was no mention of his previous claim that the Soviets have achieved military superiority.

The president called on the new Soviet leadership to show "by deeds, as well as words" a sincere commitment to the family of nations. He added a general statement that "Responsible members of the world community do not threaten or invade their neighbors, and they restrain their allies from aggression." He did not say exactly who or what he had in mind, or even that there have been recent breaches of these high principles.

It was a speech of continuity with long-established foreign policies of previous administrations, with the issue in Central America no longer one of drawing the line against communism, but of "a partnership for peace, prosperity and democracy" and the program of U.S. foreign aid "a critical investment in the future of the human race."

Reagan even discovered Jimmy Carter, pledging that in the Middle East he will "carry on the peace process begun so promisingly at Camp David."

Neither the antecedents nor the operational significance of this remarkable change were addressed last night by White House briefers, but some elements of the answers were clear enough.

Since last January in Washington, Alexander M. Haig Jr. has been replaced by George P. Shultz at the helm of U.S. diplomacy. A general was replaced by an economist; a man who thrives on confrontation, high visibility and swift maneuver was replaced by a professional mediator who operates by creating consensus in back rooms.

In the Soviet Union, Leonid I. Brezhnev was replaced by Yuri V. Andropov, bringing a steed of greater vigor, if not a horse of a different color, to the leadership in Moscow. Although the U.S. administration does not yet see substantive changes flowing from the new Soviet leadership, there is no doubt that Moscow's new activism is a force to be reckoned with in the world.

The main international battleground at the moment is western Europe, a fact that Reagan alluded to last night in saying that "allied steadfastness remains a key to achieving arms reductions."

The European publics and a number of their leaders were alarmed by his previous rhetoric, fearful that he was bent on an East-West confrontation that would shatter the postwar peace in their own front yard. The new tone is meant, in part, to allay those fears.

Another new element since last year's address is the rise of the global economic crisis to the forefront of White House concern. To deal with it, the administration will seek $10 billion to $15 billion from Congress in this year of stringency in order to support the international economy.

That dictates a bipartisan effort, moderate explanations and a nod to the International Monetary Fund, hardly a familiar topic in a State of the Union address.

It is unclear to what extent last night's speech presages a substantive shift in Reagan's main international policies in the remaining two years of his term. For reasons of "realism" and "prudence," two key words last night, what the president said about foreign policy was drastically different from his earlier statements.