The Soviet Union, which for months after Mao Tse-tung's death last September sought to improve relations with his successors, today excoriated China's new leaders as expansionist, militarists and no better than Mao.

The attack, in an authoritative article spread acorss two pages in the Communist Party newspaper, Pravda, for the first time assails new Chinese Communist Party leader Hua Kuo-feng by name . It also provides a definitive answer to one of the main questions on the international scene for many years: Would the demise of Mao end the long and bitter enmity between the two Communist giants?

The answer for now is clearly that it did not.

Indeed, the situation appears somewhat worse than before, when th Kremlin could look forward to the upheaval of Mao's passing as a chance to make headway. But now, short of a fundamental policy turnabout in Peking or a similarly basic shift of sentiment in Moscow, Sino-Soviet relations seem frozen and could even deteriorate further.

"The Chinese government's stand," Pravda asserted, "is of a purely negative and often provacative character on all vital matters of international relations."

It added: "It has long been clear to any unbiased person that the purpose behind (Peking's anti-Soviet statements) is to justify China's enormous arms spending and to distract world attention from Peking's preparatlons to carry through its expansionist plans."

Within hours of Mao's death Sept. 9, the Soviets ceased all anti-Chinese polemics and then made a series of gestures to Peking - all of them spurned - aimed at giving impetus to talks on the two countries' territorial and political differences.

While the Kremlin's conciliatory language did not contain any substantive concessions, Peking could have responded by similarly lowering the ideological temperature. Mao's successor, Hua Kuo-feng, immediately resumed vilification of the Soviets, however, calling them imperialists and a grave threat to world peace.

[China's Vice Minister of Foreign Affairs Yu Chan said in an interview published Saturday by the West Germany newspaper Die Welt that the world's most serious problem is the expansionist policy of the Soviet Union, Reuter reported from Bonn].

During the winter the Soviets gradually began to respond with expressions of regret over the Chinese attitude, always leaving open, however, the possibility of improvement. Today's article does not contain a single such qualifier.

As the conclusion to its vituperation - which is vastly harsher, for instance, than anything said about the United States even in the current period of strain - Pravda quotes a passage from Communist Party leader Leonid Brezhnev's keynote address to the 25th Party Congress in February 1976:

"Peking's frantic attempts to torpedo detente, to obstruct disarmament, to breed suspicion and hostility between states, its efforts to provoke a world war . . . present a great danger for all peace-loving peoples . . . We shall continue to repulse this in cendiary policy and to protect the interests of the Soviet state, the Social

Brezhnev's remarks then added that the Soviet Union was prepared to norist community and the world Communist movement." [TEXT OMITED FROM SOURCE] malize its relations with China in "accordance with the principles of peaceful coexistence." Today's article did not even include that tepid modifier.

Diplomatic analysts noted that the article carries the pseudonymous signature "I, Alexandrov" that is always on major Soviet pronouncements concerning China. "There is no question that this marks the formal end of any post-Mao uncertainty in the Kremlin," said one specialist.

The timing does not appear connected with any specific event, but one diplomat speculated that the Soviets might be signling the United States that they would regard a Sino-American entente as a direct threat to their security.

"Certain Western circles," said Pravda, take heart from Chinese anti-Sovietism and "delude themselves with the hope that they would be able to ward off Pekin's expansionism from themselves and channel it to a different direction. They seem to forget the bitter lessons of recent history when pacification of an aggressor brought on a heavy catastrophe for the pacifiers themselves and for world peace."In that remark the Soviets are plainly equating China with Hitler's Germany and the United States, particularly, with European appeasers - about as strong an analogy as the Kremlin can make.