A gloomy asessment of prospects for a new pact to curb strategic arms came today from the authoritative International Institute for Strategic Studies.

The director of the private research group, Christoph Bertram, warned that fast-changing weapons technology has ovetaken existing agreements that merely limit the number of weapons.

What is needed he said, is a Soviet American deal to meet the problem of quality by curbing military missions rather than the number of nuclear arms. He cited as an example the ear her agreement to limit deployment of the anti-ballistic missile.

Instead, Bertram observed, the existing 1972 pact puts a ceiling on the number of permissible weapons. This deal runs out on Oct. 3, and Bertram and his staff predicted that Washington and Moscow would agree only to extend it.

The institute staff observed that an ironic consequence of the focus on numbers has been the stimulus for a race in qualitative improvements. The experts said Soviet missiles are now so accurate that they could destroy the American missiles in their silos. The United States, in turn, has improved the accuracy of its missiles to an even greater degree and developed new weapons such as the low-flying cruise missile taht further complicate agreement.

The IISS is a highly esteemed think-tank that products an annual catalogue of military strength in all countries. The institute's excellent contacts with Western military agencies make its reports a key reference document. Bertram and his staff based their judgements on the new report issued today.

The United States, Bertram said, has still not fixed its policy to cope with the fact that improved Soviet weapons might tempt Moscow to strike first and wipe out American Missiles, Washington, he said, could concluded that such a move is unrealistic because the United States could still destroy Russian cities with untouched missiles launched from submarines.

But since this would then place Ameican cities at risk. Bertram and his staff expressed doubt that it would be the course adopted. Other alternatives listed by the HSS team were developing enough missiles to destroy the Soviet land-based army or mounting the U.S. nuclear missiles on a track to keep them moving constantly.

The central concern of the annual report is the matchup between the forces of NATO and the Warsaw Pact. "An overall balance can be said to exist today," the study concluded, but "the pattern is one of a military balance moving against the West."

Traditionally, the report said, NATO has relied on technically superior weapons to overcome its inferiority in men, tanks and planes in Europe. But this "qualitative superiority is now being eroded" by new Soviet equipment NATO is still modernizing, but the PACT countries have "been modernizing faster and expanding as well," it added.

The IISS said that some Soviet weapons, such as surface-to-air missiles, some armored vehicles and artillery are already superior to NATO's, and the Russians are also closing the gap in tactical aircraft.

As a measure of the Soviet numerical advantage, the report noted that Moscow maintains the equivalent of 70 divisions and 20,500 tanks in northern and central Europe to 27 divisions and 7,000 tanks for NATO.

In the south, NATO has 37 divisions to 33 for the Communists, but it has only 4,000 tanks compared to 6,700 in the Pact countries.

The report observed, however, that the political reliability of soldiers from Moscow's allies is in doubt. It concluded, "the overall balance is such as to make military aggression appear unattractive."

The study also saw a major shift in China's arms policy with the arrest of Chairman Mao's widow and the "Gang of Four." The study said that the People's Liberation Army "was probably the key factor" in the rise to power of premier Hua Kuo-Feng and the army strongly opposed the "Grang of Four" doctrine that had held that men are more important than weapons.

As a result, the institute expects China to seek Western technology to modernize equipment, mostly 10 to 20 years out of date.

China is thought to have stockpiled several hundred nuclear weapons, capable of reaching much of the Soviet Union and Asia. Peking is also believed to be developing an intercontinental ballistic missile with a range of 8,000 miles.