The ousted Pol Pot government, supported by China, today won an important first round in the battle to represent Cambodia at the United Nations despite strong opposition from the Soviet Union.

The credentials committee voted 6 to 3 to recommend that the 34th General Assembly seat Pol Pot's representative. The 152-member General Assembly will take up the problem Friday and, in the view of informed diplomats here, will probably accept the committee's recommendation.

China, the United States, Belgium, Ecuador, Pakistan and Senegal voted for Pol Pot. The Soviet Union, the Congo and Panama voted no.

The Soviet Union suffered a second defeat when the general committee voted 19 to 5 to place the question of events in Cambodia on the General Assembly's agenda. The Soviets and their allies had tried to head off General Assembly consideration of the Vietnamese invasion.

A vote to replace Pol Pot's delegates with those sent to the United Nations by the Heng Samrin government -- installed in Phnom Penh after a Vietnamese military invasion drove Pol Pot into the countryside last January -- would give tacit support to foreign invasions, which most nations hesitate to do.

The choice between rival claimants is a direct Sino-Soviet confrontation, but presents other nations with what many of them consider a distasteful decision.

By voting to seat Pol Pot's representatives, members give support to a government whose brutal treatment of its people after coming to power in 1975 horrified much of the world.

U.S. representative Robert Rosenstock said, "History contains few more abhorrent examples" of human rights abuses than the Pol Pot regime. U.S. officials made clear that U.S. support for the Pol Pot claim does not carry with it any implied approval or recognition of the government fighting a guerilla struggle to regain power in Cambodia.

Chou Nan, the Chinese delegate, said the matter before the credentials committee was "the major principle of supporting or opposing the occupation of territory by foreign powers."

Heng Samrin "is propped up single-handedly by Vietnamese authorities at bayonet point" and is "an outright puppet," the Chinese delegate said. There are an estimated 200,000 Vietnamese troops in Cambodia.

The Soviet Union did not demand that Heng Samrin's representatives be seated, but said it would support a proposal put forward by the Congo that the Cambodian seat on the General Assembly be left vacant.

The empty seat proposal was accepted by the Havana conference of nonaligned nations earlier this month, but diplomats who have been surveying General Assembly delegates say the Pol Pot government seems to have the majority vote it needs to remain in the United Nations.

The majority of U.N. members appears to agree with Pakistan's delegate Niaz A. Niak who told the credentials committee that "human rights cannot be used to justify foreign invasion." The principle of territorial integrity is so important to so many nations which have hostile and powerful neighbors that they are reluctant to approved armed conquests if there is any evidence, no matter how slight, that the overthrown government still has a toehold within its country.

One exception has been Tanzania's invasion of Uganda which toppled Idi Amin earlier this year. While Vietnam was condemned for ending the butchery of Pol Pot, few voices protested the Tanzanian action against Amin's brutal rule.

The Tanzanian invasion is not the iscause no complaints have reached the assembly from Uganda. Assembly president Salim Ahmed Salim, himself a Tanzanian, told reporters he has seen no efforts to link the two invasions in debate here.