China put Vietnam on notice yesterday that it faces "grave danger" if it continues military raids into Thailand.

The Foreign Ministry in Peking said China would "resolutely support" Thailand's efforts to defend its sovereignty.

The Chinese statement, which diplomatic sources here viewed as tough but not explicitly threatening, came after U.S. Secretary of State Edmund Muskie condemned the Vietnamese incursion and said the United States was in close consultation with Thailand.

Activity along the Thailand-Cambodia border was relatively quiet yesterday. Most Vietnamese forces appeared to have withdrawn into Cambodia, and Thai troops at forward posts reported no major clashes.

Thai artillery shelled Vietnamese positions along the frontier sporadically during the day while foreign medics continued to evacuate hundreds of wounded refugees from camps that had been overrun. [Details on page A15.]

China and Vietnam fought a one-month undeclared war in February and March of 1979 after Vietnam ousted the Chinese-allied Cambodian regime of Pol Pot in a lightning military conquest. Chinese forces occupied four provincial capitals in northern Vietnam before withdrawing.

The Chinese, who view Vietnam's presence in Cambodia as an extension of Soviet influence in the region, have cooperated increasingly with Thailand over the last year on security matters.

"The Thai government has solemnly declared its determination to defend Thailand's sovereignty and territorial integrity," the Chinese statement said yesterday.

"The Chinese government and people firmly support this just stand of the Thai government, and forcefully call on the Vietnamese authorities to stop their aggression at once. . . . We hereby call the attention of the Vietnamese authorities to the grave danger involved if they persist in military adventures in disregard of the just demands of the international community."

State Department spokesman Hodding Carter said yesterday the Thai government has asked the United States for increased security assistance and accelerated equipment deliveries. He said the requests will be reviewed on an urgent basis and probably be approved.

He also read the statement from Muskie, who is attending a NATO meeting in Turkey. In it, Muskie said the Vietnamese action threatens the "peace, security, and stability of the entire region" and appealed to the Vietnamese to refrain from "any further aggressive action."

Muskie also called on the Soviet Union, "without whose support these actions would not be possible, to use its influence to bring an end to the present conflict."

In Bangkok, Vietnamese Foreign Minister Nguyen Co Thach was greeted by jeering demonstrators when he arrived for an unofficial two-day stopover on his way home from Indonesia. The visit had been scheduled two weeks ago, but because of the tensions no Thai diplomats were on hand to greet him. There was speculation private meetings would be arranged to discuss ways of defusing the crisis.

Vietnam and Cambodia contend that Thailand provoked the attacks by allowing Khmer Rouge forces opposed to the Hanoi-backed government in Phnom Pehn to use Thailand as a springboard for guerrilla operations in Cambodia. Thailand continues to recognize the Pol Pot government.

Many diplomats in Thailand also believe the Chinese Embassy is actively assisting Khmer Rouge troops in the field, using sympathetic Thai-Chinese merchants as conduits for food, medicine and other supplies.

Unitl recent years China had actively supported Communist insurgents in Thailand in their efforts to overthrow the military-dominated government in Bangkok. But common interests have persuaded China to put ideology aside.

In July of 1979 Peking silenced the Voice of the Thai People, a radio station in southern China that broadcast the views of the Communist Party of Thailand. Chinese leaders offered visiting Thais a pledge of aid against Vietnamese attacks. And last December China made large amounts of oil and fuel available to Thailand at "friendship prices."