China and Japan yesterday went ahead and signed a peace and friendship treaty in Peking despite the bitter opposition of the Soviet Union.

An authoritative Tass commentary, issued shortly after the signing of the treaty, denounced the pact as an anti-Soviet document designed to enable China to "widen the sphere of its influence" in Asia.

In Washington, however, the State Department welcomed the conclusion of the Sino-Japanese treaty, saying it promoted Asian peace and stability.

The Kremlin's unhappiness over the conclusion of the Sino-Japanese pact appeared primarily directed at Peking, and reflects Moscow's growing uneasiness over what is viewed here as an increasingly active Chinese diplomatic effort to build a broad "united front" encircling the Soviet Union.

The timing of the treaty signing, coming only a week before Chinese Chairman Hua Kuo-feng is scheduled to leave on an unprecedented visit to Romania and Yugoslavia, only adds to the Kremlin's fears.

Another authoritative commentary published yesterday in the Communist Party daily Pravda implicitly denounced Hua's impending visits to Moscow's European neighbors as an effort to penetrate Eastern Europe, and turn the Balkans into a "powder keg."

The Soviets made it clear yesterday that they are far from persuaded by Japan's insistence that the new Sino-Japanese treaty is not directed against Moscow.

They seemed unlikely to find comfort, moreover, in reports from Peking last night that China would soon scrap the 1950 Sino-Soviet treaty.

This treaty, concluded in 1950 when the Soviet Union and China were still on good terms, describes Japan as "the common enemy."

Japanese Foreign Minister Sunao Sonoda said last night that "it is my strong impression from my meetings with the Chinese leaders that the government of China will take necessary measures to terminate this [Sino-Soviet] treaty in April next year."

The Tass commentary yesterday was far more critical of China than Japan, condemning the Chinese leaders as people with "aggressive aspirations." The commentary said, however, that by "capitulating before Peking's insistence on the inclusion of an anti-hegemony" clause in the treaty, Japan may have damaged its national interests and its relations with the Soviet Union.

Diplomatic observers said this reaction, while reflecting Soviet anxieties, does not suggest that Moscow contemplates any serious retaliatory steps against Japan, one of the Soviet Union's key trading partners.

Attacking the "notorious" clause on hegemony, the Tass commentary said that "the article is directed against the Soviet Union, which was repeatedly noted in speeches by Peking leaders themselves."

The term "hegemony" in Communist diplomatic language refers to domination of a country or region by another country. The Tass commentary quoted China's Foreign Minister Huang Hua as saying the common opposition to "hegemonism" is the "basis of the Sino-Japanese treaty." The Chinese, in particular, have been conducting a campaign against Soviet "hegemony."

Tass said it is clear that "the treaty is in conflict with the interests of peace and detente, it is fraught with tremendous dangers primarily to the peoples of Southeast Asia, who have already long been target of aggressive aspirations of Peking leaders.

"Peaceable nations cannot pass over the fact that the conclusion of the Sino-Japanese treaty is fraught with danger to stability in Asia. They will not allow the Peking hegemonists to recarve the map of that region and widen the spliere of its influence with the aid of any of [their] allies. The selfish interests of the great Han chauvinists are doomed to failure."

Tass said that the Japanese "capitulated to Peking" although they were "aware of the danger of including into the treaty an article which is of an openly anti-Soviet character and serves the selfish interests" of Peking leaders.

Before the treaty was signed in Peking, Tass said that the Chinese were openly striving for domination of Southeast Asia and had started disputes with nearly all their immediate neighbors. China had territorial claims in most and had repeatedly resorted to force, it said.