The graying, heavyset man with military medals glittering on his suit jacket and a hearing aid peking out behind his left ear turned slowly and cautiously towards his victor and spoke of atomic weapons. The first time one of those things is fired in anger, he said, everything is lost. The warring nations would never be able to put matters back together.

In this sobering moment Monday eventing in this third floor officeat the Kremlin, where generations of Czars decreed life or death for generations of Russians, Soviet leader Lesnid Brehnev and his guest, Secretary of State Cyrus Vance, got away from the technicalities and went to the heart of the superpower negotiations on control of stategic nuclear arms.

The 71-year-old, infirm Soviet leader, Vance reported later, seems to have decided that a strategic arms agreement is the legacy he would like to leave behind. He is deeply and personally interested, as is his opposite number in the White House, 5,000 miles and 15 minutes away by inter-continental ballistic millile.

According to informed American sources, more progress than was made known publicly marked the two days of Soviet-American talks on a new Strategic Arms Limitation Treaty (SALT). "Substantial progress" was reportedly made on resolving one of the handful of outstanding issues. Sets of new ideas presented by both sides suggest possibilities for a movement towarda final accord.

Vance is reported to believe that the next round of talks with the Soviet "should" produce enough agreement to take the nearly completed treaty to summit meeting of Brezhnev and President Carter. The main problem is that neither side wants to be the last to make a concession, an indication that more pride and politics is involved than strategic nuclear arms concerns.

Soviet military career officers, like their American counterparts, are fixed on the comparative advantage and disadvantage of the final equation. As in the American case, however, the Soviet political leadership appears determined to come to agreement with the other side.

At several key points during the lengthly sessions between Vance and Foreign Minister Andrel Gromyko, the Soviet diplomat called for a recess to ontain advice by telephone. The belief of the American team, on the basic of the context, was that Gromyko consulted higher civilian authority - that is Brezhnev - rather than the military staff.

In Vance's two earlier meetings with Brezhnev, in March 1977 and April 1978, the two sides, to a large degree, were "talking past each other" in dicussions of the SALT II treaty regional disputes in Africa and the Middle East which threaten confrontations of the superpowers.

This time is said to have been significantly different. Vance, who returned to Washington yesterday and reported immediately to the White House, publicly labeled the session with Soviet leader "friendly and cordial" in atmosphere. He noted a greater degree than any time in recent stronger Soviet belief that the superpowere must find ways to work together.

The atmosphere and attitude in Brezhnev's Kremlin office are paradoxical because the Soviets are feeling isolated and embarrassed to a greater degree that any time in recent memory. At Camp David Carter arranged an Egyptian-Israeli peace which changes the geopolitical map of the Middle East, with no role for the Soviets. China and Japan, with U. S. encouragement, have signed a possibly historic peace and friendship treaty. The French, on the eve of Gromyko's visit to Paris, announced the first major European arms sales to the hated chinese.

The possibility the Soviets might lash out in frustration and anger cannot be foreclosed, but for the mement there is no sign of this happening. Carter recently called on Brezhnev to help put out the fires of civil war in Lebanon, and the Soviet leader instantly agreed. This week the Soviets withdrew their objections to a renewal od the U. N. peacekeeping mandate in the Sinai, and agreed to a compromise nine-month renewal with no change in the terms.