Soviet leader Leonid Brezhnev, in apparent good health, marked his new international status as president of the U.S.S.R. today by holding a Kremlin reception for ambassadors of more that 90 countries and telling them they must take "unbiased assesment of any concrete proposals or actions by the Soviet Union."

"One Western diplomat who had dealt with Brezhnev many time called the Kremlin leader's performance before envoys eager to judge for themselves the state of his health a "tour de force."

The Soviet chief did not mention any of the conflicts that have arisen between the U.S.S.R. and the Carter asked the diplomats to "convey to your heads of states and leaders" that the Soviet Union seeks peaceful solution to international tensions.

"It is our belief, our firm belief," he said, "that realism in politics and the will for detente and progress will utlimately triumph and mankind will be able to step into the 21st Century in the conditions of peace stable never before, and we shall do all in our power to see it come true."

he reception formally told the outside world that Brezhnev now stands along at the pinnacle of the Soviet government - president of the country as well as general secretary of the Communist Party, and firmly on the same protocal level as Western counterparts such as President Carter.

Brezhnev, whom French diplomats last week reported to be in declining health, spent about 75 minutes at the reception, shaking hands and chatting amiably with each foreign representative. But Brezhnev reportedly spent only a moment with U.S. Ambassador Malcolm Toon, with whom he met for an hour and 40 minutes Tuesday in a spirited discussion of human rights, strategic arms talks and other issues dividing the superpowers. Today, Brezhnev reportedly told Toon pleasantly. "We've already had a long talk and I have nothing more to add."

Western diplomatic sources said Brezhnev's diction was better today than it has been for some time. There have been persistent rumors in the West that Brezhnev is suffering from a serious chronic jaw ailment that flares up intermittently, causing his speech to deteriorate. Today, his voice was said to have the clarity and timbre of an elderly but robust man who was enjoying himself.

By the latest count, 94 nations are represented by diplomatic missions in the Soviet capital. Today, their representatives gathered at a respectful distance across the reception room from their host, and those in the rear craned for a clear view of the new chief of state, who has run the country for more than 10 years.

Western Diplomats said today that at their meeting Tuesday. Brezhnev and Toon discussed the stalled strategic arms talks, the stalemated peace efforts in the Middle East, and languishing U.S.-Soviet trade as well was the human rights issue.

The Carter administration has championed the cause of the small group of dissidents who are still vocal here after nearly five years of harassment, imprisonment and exile by the government. Western diplomatic sources said they believe that if the Soviets conduct a show trial in the case of Anatoli Scharansky, who reportedly has been charged with the capital crime of treason, relations between the kremlin and Western nations will be more difficult.

A number of Soviet human rights activists are in jail and facing charges.

The White House has expressed concern at such arrests and the Soviets have vehemently objected to such American gestures, saying the Americans are meddling in internal affairs of the Soviet Union.

Later today, sources reported, Toon met with Vasily V. Kuznetsov, deputy foreign minister, for what was said to be " a good exchange of views" on the Middle East. It was one of a continuing series of consultations between the two countries on major problems between them.

Tass, the official Soviet news agency, continued its attack of recent weeks on the Carter administration today, criticizing Paul Warnke, director of the Arms Control and Disarmament Agency, for "acting in the same spirits as certain circles in the U.S. that have no wish to solve problems of curbing the arms race."