South African Prime Minister John Vorster pledged today that his government would not succumb to external pressures to push Rhodesia into accepting the Anglo-American plan for transition to black majority rule - "a solution dictated to them from outside."

The announcement, made in Parliament, may well be the death blow to the settlement efforts of the U.S. and British governments, who were counting on the South Africans to use their everage on Rhodesian Prime Minister lan Smith to renew negotiations.

As Rhoesia's only ally and link to the outside world, South Africa has the political and ecomomic power to make its landlocked neghbor cooperate with any plan, including the British proposals Smith rejected Monday.

Vorster's statement will also allow the Rhodesian government to pursue its plan to go it alone - negotiate with moderate Africans on terms for transition to majority rule.

The move may come as a surprise to the United States and Britain.

Earlier this week, the new U.S. Ambassador to the United Nations, Andrew Young said, "I am confident that the forces for negotiation will regroup. Rhodesia cannot survive without South Africa - and if South Africa says negotiate . . . Rhodesia will."

Young added that he felt South Africa would want to use its leverage because it realized that failure could-bring chaos to southern Africa.

In his speech during the no-confidence debate opening the new parliamentary session, Vorster said: "Demands to shut our borders and impose boycotts (against Rhodesia) cannot be acceded to because they are contrary to the policy of this government." "Pressure will be exerted on South Africa to an increasing degree to exert pressures on others. I would rather bear the consequences," the prime minister said in an obvious reference to the U.S. government.

"It is wrong to misuse that sort of power to force a man to do something against his will."

Vorster said demands had been made continually by speakers at the United Nations, "certain U.S. Senate circles" and elsewhere to put pressure on the Rhodesian government.

But the Suth African leader said to do so would be to act "dishonorably," since it meant forcing Rhodesia to submit to terms dictated by militant black African governments.

There has been some speculation here that Vorster took this position because of his own government's precarious position, which could come under new pressures from the new U.S. administration.

The "noises," as they are called here, from the Carter administration about policy changes on South Africa could have led the Vorster government to feel it will get nothing from Washinton in return for exercising pressure on Rhodesia.

The theory is supported at least partially by a speech Vorster made New Year's Eve, when he warned that South Africa could no longer rely on the West for support and would have to face the future alone.

He reiterated the message today, claiming South Africa was under tremendous pressure from both the West and the Communist bloc.

"We are under exceptional pressure from the Marxist world because of our strategic position necessitates them absorbing us. If they should succeed it would give them sole possession of 90 per cent of the world's platinum resources, 75 per cent of the world's manganese, 80 per cent of its gold, 80 per cent of its diamonds and 80 per cent of its vanadium."

Vorster warned that a Communist monopoly of the world's oil supplies coupled with a monopoly of natural resources would place the West in a "precarius position." The government won the confidence vote 122-47

Vorster also took a stiff line on settlement of the Namibia (Southwest Africa) dispute, the positon of coloreds ( people of mixed race) in South Africa, and the question of increased power for blacks.

On Namibia, he said there were increasing pressures on his government to hold negotiations with the militant Soutwest African Peoples Oraganization (SWAPO). Which is now wating a guerrilla campaign in northern Namibia from bases in Angola, on handing over power of the disputed territory South Africa has administered since World War II.

The prime minister asked rhetorically: "Are we willing to make this sacrifice?" indicating his government backs the current constitutional negotiatians among Minibia's 11 ethnic groups as the only way of moving toward independence of the territory.The United States has been pressuring Vorster to negotiate with SWAPO to end the dispute.

On the status of South Africa's 2.3 million coloreds, Vorster pledged that his government had no intention of giving them the vote. The National Party government removed the coloreds from the voter kolls in 1956.

Instead, he said he planned to meet with the Asia nand colored community leaders in March to discuss a "cabinet council" made up of the two minority groups, which would eventually take over administration of their own affairs.

Vorster also strongly reaffirmed his government's policy of separate development, which will eventually carve up South Africa into nine small African states with more than 80 per cant of the land remaining in white hands.

He indicated that there was no question that blacks remaining in the white area would ever gain political rights. The policy means that all of South Africa's 18 million blacks will eventually become citizens of one of the nine smaller African countries, and thus aliens in South Africa.

The prime minister did not mention the race riots the sputtered on and off for six months last year - during which over 500 were killed - although he said "more and more" was being done to alleviate African grievances.