Soviet Foreign Minister Andrei Gromyko, in a policy speech yesterday to the United Nations General Assembly, attacked "falsehoods" and "propaganda" about Russians and Cubans. He suggested that the United States should admit to creating an artificial issue and hinted that the dispute should be considered closed.

President Carter, in a "town meeting" last night in Queens, reiterated the U.S. contention that a Soviet force in Cuba is a combat unit, despite Soviet denials.Carter said he does not know if negotiations on the matter will be successful but declared he will take action "to change the status quo" and report to the nation, probably within the next week, if current talks fail.

He refused to say what action he is planning but said, "I believe you'll be satisfied when I make my report to the nation."

White House officials were unable to expand on Carter's plans for the report. The president also reiterated that the Soviet brigade does not pose a threat to U.S. security but said it is unacceptable to the United States.

In unusually strong language, Carter called Cuba "a puppet" and "a Soviet surrogate around the world" that acts completely in accord with Moscow's policies.

The airing of opposing and seemingly rigid positions came one day after Gromyko and Secretary of State Cyrus R. Vance met here Monday in the sixth of a series of U.S.-Soviet discussion of the issue.

Informed sources said Gromyko offered no concessions in the private talks, which are scheduled to continue Thursday afternoon. It was unclear, however, whether his diplomatic posture and public statements of the past two days represent the final Soviet position.

State Department spokesman Hodding Carter would say only that "we are still in the midst of discussions with the Soviet Union on the Soviet brigade in Cuba." His statement on behalf of Vance suggested a continuing hope for a Soviet shift toward compromise in the forthcoming talks.

Gromyko had been scheduled to leave New York for home at the end of this week, and there was no word whether his stay will be extended. Failure to make progress toward a resolution of the dispute or to establish a negotiating path that holds promise of an eventual settlement would place Senate approval of the strategic arms limitation treaty (SALT II) in grave jeopardy as well as trigger U.S. compensatory actions.

Gromyko's General Assembly address today, like that of Vance in the same forum 24 hours before, included a brief section that addressed the Soviet brigade issue without explicitly saying so. Thus the Russian, like Vance, took a strong position without openly addressing the issue under discussion in secret talks of the nuclear superpowers.

Without mentioning the combat brigade, Gromyko charged that "all sorts of falsehoods are being piled up concerning the polices of Cuba and the Soviet Union.

"But the truth is that this propaganda is totally without foundation. It has no real basis and is indeed based on falsehoods. The Soviet Union and Cuba have already so declared."

Without saying to whom it was addressed, the top Soviet diplomat added: "Our advice on this score is simple: it is high time you honestly admit this whole matter is artificial and is proclaimed to be closed."

In Washington, reaction to the Gromko speech was harsh. Sen. Frank Church (D-Idaho), chairman of the Senate Foreign Relations Committee, recommended that his committee delay sending the SALT treaty to the Senate floor until something is done about the troops in Cuba.

Senate Republican leader Howard H. Barker of Tenessee said he was ASTONISHED" by Gromko's speech. "There is simply no basis for doubting that the Russians have a fully equipped, fully manned combat brigade in Cuba," he said.

Gromyko introduced his comments by saying that "a huge number of spurious films, books, articles and speeches of politicians and quasipoliticians are produced to make people believe the fistitious stores about the source of a threat to the peace."

The Soviet Union maintained in a front-page Pravda editorial two weeks ago that its troops constitute a long-standing "training center" for Cuban forces, not a combat brigade as the United States has charged. Gromyko is reported to have stuck to this Soviet position during his meeting with Vance late Monday.

State Department officials left open the possibility that Vance might shift his weekend travel plans and other appointments to accommodate more meetings with Gromyko if such action is justified by progress in their talks Thursday. Although there is no plan for Gromyko to see President Carter, as has been customary during the Soviet minister's visits to the United Nations, this too has not been ruled out if progress can be made on the Cuban troops issue.

U.S. officials denied a report that Washington has set a deadline of this weekend on negotiations over the brigade issue. There is "no commitment or basis for such a deadline," an official said.

Last Thursday, Vance presented several suggestions to the Kremlin through Soviet Ambassador Anatoliy F. Dobrynin, ranging from withdrawal of the Soviet brigade to face-saving arrangements under which the Soviet force would be stripped of its "combat capability" even though individual solidiers remained.

In a separate section of his address, Gromyko stressed the importance of U.S.-Soviet ties, saying durability and stability of world peace depends "to an important extent on the state of relations between the Soviet Union and The United States."

Soviet leaders seek normal and even friendly relations with the United States, Gromyko said. He added that this requires adherence to principles of "peaceful coexistence" and "noninterference in the affairs of others."

Gromyko declared, "We shall not allow anybody to meddle in our internal affairs. Concern for Soviet-American relations is a matter for both sides. It is only on this basis that the relations between the U.S.S.R. and the United States can develop successfully."

Gromyko praised SALT II as proof that it is possible for Washington and Moscow to agree on the most difficult questions "given the good will and readiness to take into account each other's legitimate interests." The qualifications appear to be still another indication of Soviet sensitivity about the U.S. posture at present.

Gromyko depicted the Soviet Union as a nation striving for disarmament despite impediments introduced by the United States and other Western powers in several sets of negotiations, including the nuclear test ban talks, U.S.-Soviet talks on demilitarization of the Indian Ocean and the Vienna talks on mutual force reductions in Europe.

He described East-West-detente as 'the positive trend in international affairs" during the 1970s and said "the Soviet Union stood at its cradle."

Nonetheless, he added, "There still are people in the world today who make a wry face at the word detente like a hungry cat in a kitchen garden at the taste of cucumber."

As expected, Gromyko made blunt attacks on China, the Soviet Union's arch rival, charging that Peking committed aggresion by invading Vietnam early this year. Nothing was said about the Vietnamese invasion of Cambodia except that "the blood-thristy and murderous regime of Pol Pot . . . has been done away with" and will not return.

Gromyko attacked "the artifically whipped-up propaganda campaign concerning Indochinese refugees," saying it is directed against Vietnam.

He praised Soviet allies such as Cuba and Afghanistan and expressed the hope for continued development of Soviet relations with a long list of Western European and Third World countries.