MOSCOW, NOV. 30 -- Soviet leader Mikhail Gorbachev, acknowledging for the first time that Soviet scientists are engaged in research on space-based missile defenses, said in an American television interview that President Reagan's Strategic Defense Initiative is "not a subject for negotiations" as long as it does not violate the 1972 Anti-Ballistic Missile (ABM) treaty.

Gorbachev stressed, however, that unlike the United States, the Soviet Union had no intention of building such a space defense system.

The Communist Party leader, in a wide-ranging interview with NBC correspondent Tom Brokaw broadcast a week before arrival in Washington for a third meeting with President Reagan, delivered a lively, energetic defense of policies ranging from human rights to arms control, from agriculture to the role of women. Of his wife, Raisa, Gorbachev said twice, "We discuss everything."

Gorbachev also appealed for a new start in the Soviet-American relationship, saying that he was going to Washington to discuss ways that the two superpowers could return to their former wartime status as allies in coping with the modern world's troubles.

"There's so many problems in the world!" he said. "Can't we join our efforts, . . . pool the enormous might of our countries' economic, intellectual capacities to resolve all these problems?"

Signaling a flexible approach on key arms control issues, Gorbachev said he believes "it is possible to do a lot of work" on arms control with the Reagan administration after the two leaders sign a treaty eliminating U.S. and Soviet medium- and shorter-range missiles in Europe and Asia.

The Soviet leader said he is prepared to accept an agreement cutting U.S. and Soviet intercontinental missiles by 50 percent if both sides agree to strict compliance with the ABM treaty.

Gorbachev's expressed willingness to consent to an arms accord that would permit Reagan's "Star Wars" research program to continue, and his admission that Soviet scientists are pursuing similar work, suggested the outlines of a compromise that would allow research to proceed on both sides within the confines of the ABM treaty.

Such a compromise was first suggested by Soviet Foreign Minister Eduard Shevardnadze in a September meeting in Washington with Secretary of State George P. Shultz and Reagan.

The Soviet leader's remarks on SDI appeared to culminate a marked shift over the past year in the Kremlin's position on Reagan's plans for a space-based missile defense.

In that time, the Soviets have moved from harsh public attacks against the "militarization of space" to an acceptance of research programs that could offer acceptable terms to the Reagan administration for deep cuts in strategic weapons.

"Practically, the Soviet Union is doing all that the United States is doing, and I guess we are engaged in research, basic research, which relates to those aspects which are covered by the SDI of the United States," he said.

But Gorbachev insisted that the Soviet program has not gone beyond research. "We will not build an SDI, we will not deploy SDI, and we call upon the United States to act likewise," he said.

Although he said that "the question of SDI is not a subject for negotiations," he repeated the Soviet insistence that a 50 percent cut in strategic offensive weapons would be linked to "strict observance" of the ABM treaty.

"In that degree that SDI does not run counter to the ABM treaty, let it -- let America act, let America indulge in research. Insofar as SDI does not run counter to ABM," he repeated, "that is not a subject for negotiations."

Gorbachev made it clear that the interpretation of the ABM treaty and strategic weapons cuts will dominate his three days of talks in Washington.

On cuts in strategic weapons, he said the Soviet Union would talk "about levels and sublevels," an area where the two sides moved closer together in October during a visit to Moscow by Shultz. Then, for the first time, Gorbachev agreed to differentiate the cuts as they applied to specific categories of weapons, setting goals close to the U.S. position.

In the interview, he indicated that further movement on strategic cuts -- which he called "the very core of Soviet-American relations" -- could come at the summit. "We have some steps that we could take to meet the American position halfway," he said. "And we've already taken some."

"There are real prospects ahead of us," he said. " . . . We believe that it is possible to do a lot of work with this present administration so as to -- so that we could make headway on this major direction in the area of arms control."

Asked about the prospect of troop reductions in Europe, Gorbachev said, "Firstly, the Americans and the Europeans and the others should know that the Soviet Union has no intention whatsoever of attacking anybody."

He also acknowledged a "certain asymmetry both in forces and armaments" between Warsaw Pact and NATO ground forces and said, "We're prepared to address ourselves to that without delay."

In his opening comments, Gorbachev said that he has received 80,000 letters from Americans this year. "A lot in those letters has stirred me," he said, noting that many expressed hope for better relations. "The Americans say, Now, why is it -- now, why can't we be allies? . . . . we were allies at one time -- Why can't we be allies now?"

He pointed out "the emergence of a new situation" in U.S.-Soviet relations, but appealed for "greater respect for each other" and a better understanding of each other's history. The Soviet leader, who has met numerous U.S. delegations since coming to power in March 1985, said he now has "a better understanding . . . of American society than I did before I took up this job." Like other Soviets, he said, he has read American literature, "mostly . . . classics." He did not name any books.

The NBC interview, which took place on the third floor of the Kremlin, culminated two years of efforts and several round trips to Moscow by one of the network's chief representatives, former vice president Gordon Manning. The Soviet leader has traditionally given interviews to foreign correspondents on the eve of his trips to their countries. The NBC interview will be broadcast here Tuesday night.

Gesturing with his hands, at one point jabbing the air with his finger, Gorbachev gave a vigorous performance, appearing combative but not aggressive on controversial issues. Gorbachev defended the recent firing of Moscow party boss Boris Yeltsin, whose ouster prompted protests from diverse groups in society. "No," he said in answer to Brokaw's question, "there was no mistake."

He criticized both "adventurism" and "conservatism," striking the same balance between the party's opposing poles that he has in other public remarks since Yeltsin criticized top party members, accusing them of braking the pace of reform. Gorbachev also insisted that the episode, which he called "a normal process for any democracy," had not set back his program of reform, known as perestroika.

Asked about human rights policies in the Soviet Union, Gorbachev countered with a critique of the United States' record on social and economic justice and its failure to ratify international human rights agreements. "The United States is being criticized for that throughout the world," he said.

"I think there will be a lot of water passing through the Mississippi and the Volga before the U.S. Congress and the administration recognize the American people's right to their protection of their social and economic rights," he said.

Pressed on restrictive Soviet policies on emigration, he shot back with another jab, accusing the United States of "organizing . . . a brain drain" from the Soviet Union during the height of emigration in the 1970s.

He charged the United States and Canada with keeping out low-skilled immigrants from Mexico and other countries. "But as soon as in the 1970s there was especially a big flow of those who wanted to emigrate from the Soviet Union," he said. "There was one highly placed representative of the administration who declared that we've resolved the problem of mathematicians by 50 percent."

Emigration from the Soviet Union has increased over the past year. In particular, compared to 1986, Jewish emigration has risen six-fold. Gorbachev admitted that family reunification is still "a problem" that needs to be resolved, but indicated that Soviet emigration will remain tightly controlled.

On other issues, Gorbachev observed that:

He and Reagan will discuss a timetable for the withdrawal of Soviet troops from Afghanistan: "I believe that if the American administration really does sincerely want that problem to be resolved, to be closed by political means, it could be done very quickly."

Any decision to tear down the Berlin Wall would come from East Germany: "That is the sovereign right of a sovereign state, . . . to defend its and protect its choice and not to allow any interference in its domestic affairs."

The Soviet Union must "develop and improve" relations with Cuba and Nicaragua. But he scoffed at the idea that the Moscow-backed Sandinista regime in Nicaragua is a regional threat: "I have to smile when I hear that the security of the United States is being threatened by the Sandinista regime. That's not serious."

There is no role here for another party besides the Soviet Communist Party: "I see no need for any other party, and I think that is the view of our society."

Women should take part in "all spheres of life," but not at the expense of their "predestination -- that is, as keeper of the home fires of the family, guardian of the family."

Asked what he talks about with his wife, Raisa, he said: "We discuss everything." Brokaw persisted: "Including Soviet affairs at the highest level?" Gorbachev, leaning back in his chair with a slight smile on his face, said, "I think I have answered your question in toto. We discuss everything."