The unlikely trio of former president Richard M. Nixon, former Senate Republican leader Howard H. Baker Jr. and former Democratic senator and secretary of state Edmund S. Muskie held an unannounced meeting with President Reagan last September to discuss new arms control approaches to the Soviet Union.

Reagan seemed "very interested" in the trio's ideas, Baker said yesterday in comments relayed from Tokyo, where the senator, who retired in January, is on a business trip.

The meeting with Reagan was reportedly preceded by talks with Secretary of State George P. Shultz and then-White House chief of staff James A. Baker III, as well as memos sent to the administration. But the trio's ideas "never got to the Russians," said James M. Cannon, who then was chief aide to Howard Baker.

After a report in the Chicago Tribune yesterday about what the White House called "a private meeting," various participants spoke about the discussions in guarded terms.

John Taylor, a spokesman for Nixon, said they had met over a period of more than a year to discuss "arms control and Soviet-American relations in general." The latest talk took place, he said, when Nixon invited Baker and Muskie in his Saddle River, N.J., home March 27.

Muskie said that "if anything had happened as a result of the discussions it probably would be evident." More meetings may be held, said Muskie, who added that "this kind of effort can't succeed if conducted in a public spotlight."

Muskie said Walter F. Mondale, who was the Democratic presidential nominee when the three met with Reagan, was informed of the discussions. Mondale, in a separate interview, said Muskie had telephoned him last Sept. 27 -- three days after the trio's meeting with Reagan -- to tell him of the effort "to structure an approach in negotiations which might get arms control moving."

Mondale said he told Muskie he had no objection and said he never learned the details.

Several of those interviewed said the meetings were initiated by Alton Frye, Washington director of the Council on Foreign Relations, who participated in some sessions. Frye said the "very intimate process" of three-way discussions were "an intellectual effort to frame usable policy that the president may wish to consider." He declined to give details.

The meeting with Reagan took place over lunch at the Waldorf-Astoria Hotel in New York last Sept. 24 after Reagan's address to the U.N. General Assembly. Reagan called in the speech for "constructive discussions" with the Soviets.

At that time, arms negotiations had been in limbo for nearly a year because of a Soviet walkout. Shortly after the U.S. fall elections the Soviets agreed to new negotiations that began in Geneva March 12.