State Department officials said yesterday that they interpreted Soviet leader Mikhail Gorbachev's overtures to China in a speech Monday as a major bid for a broad improvement in Sino-Soviet relations and in ties with other Asian nations.

One senior official said Gorbachev's address in Vladivostok, in the Soviet Far East near Japan, was "extraordinary" in asserting Moscow's desire for a greater role in Asia and the Pacific. Another official said it was the most important Asia-oriented declaration from Moscow since the early 1980s.

Official sources particularly cited Gorbachev's announcement that a "substantial" withdrawal of Soviet troops from Mongolia is being considered and his statement that Moscow is prepared to discuss with Peking "concrete steps aimed at proportionate lowering of the level of land forces" across their common border.

The possibility of Soviet troop reductions along the Chinese border, and especially from the Mongolia area, which is on a main invasion corridor to Peking, the Chinese capital, has been the subject of considerable speculation in the past. Withdrawals from Mongolia, where 50,000 to 60,000 Soviet troops reportedly are stationed, were rumored several years ago but did not develop.

Monday's speech was reported by U.S. sources to be the first time that such a prospect was publicly announced. Gorbachev said withdrawal of "a substantial part" of the Soviet forces from Mongolia is being "examined jointly with the Mongolian leadership."

Gorbachev's stated willingness to negotiate withdrawals from elsewhere along the Sino-Soviet border, where a half-million or more Soviet troops are stationed, is also more explicit than before, officials said.

The Soviet force along the Chinese border is one of three obstacles Peking has often cited to a basic improvement in relations with its communist rival. The others are the presence of Soviet troops in Afghanistan and Soviet support for Vietnam's occupation of Cambodia.

By announcing a withdrawal of six military regiments, about 6,000 men, from Afghanistan, Gorbachev was addressing another of China's "obstacles," State Department officials noted. But this reduction is so small compared to the overall Soviet occupation force of more than 115,000 that it is deemed unlikely to impress Peking.

A commentary monitored by U.S. agencies in Hongkong yesterday from a mainland Chinese news agency said the announced Soviet withdrawal from Afghanistan "will not affect the Soviet military presence" there. However, it said "this is the first time the Soviet leadership has openly expressed the withdrawal of Soviet troops from Afghanistan and Mongolia, and the long-term rigid attitude of the Kremlin has relaxed somewhat, which is worth welcoming."

The Chinese commentary said Gorbachev offered little that is new about the conflict in Cambodia. Saying that the new Vietnamese Communist Party leader, Truong Chinh, is on "vacation" in the Soviet Union, the commentary asked, "will he talk over this issue with the Soviet leadership?"

U.S. officials said Gorbachev made what seemed to be an oblique reference to the Soviet military presence at Cam Ranh Bay in Vietnam, which has been a major concern for both Washington and Peking. If the United States should "give up" its military bases in the Philippines, Gorbachev said, "we would not leave this step unanswered."

In addition to remarks addressed to China, Gorbachev spoke of a desire to improve relations throughout the rest of Asia. He specifically proposed an Asian conference to be held in Hiroshima, Japan, similar to the European-based Helsinki meetings on East-West relations. State Department officials said the United States does not favor such a meeting under present circumstances.

Gorbachev directed considerable attention to Japan, the economic giant of Asia, and said an exchange of "top-level visits" is on the agenda of Soviet-Japanese discussions.

Japanese Prime Minister Yasuhiro Nakasone, in a television interview, said he hopes Gorbachev will visit Tokyo "at an early date." Such a visit would be "a very significant diplomatic move" by Moscow, Nakasone said.