Black nationalist leader Robert Mugabe today warmly welcomed President Carter's refusal to lift economic sanctions on Zimbabwe-Rhodesia and said his decision amounted to an American rejection of Bishop Abel Muzorewa's government.

"Our hope is that the Carter administration will persist to the end with this stand to support the complete dismantling of the Smith-Muzorewa regime and create a clear path to the transfer of power to the people of Zimbabwe as a whole," Mugabe said in a statement issued today.

In an interview before President Carter's announcement Thursday Mugabe said he was ready to consider new British proposals for ending the guerrilla war in southern Africa but virtually ruled out the possibility he ever would agree to participate in any future elections with Zimbabwe-Rhodesia's first black prime minister, Bishop Muzorewa.

He also said a new round of negotiation over Zimbabwe-Rhodesia sponsored by London and Washington would have to be held directly between the guerrillas and Britain and exclude the Muzorewa government.

"It's still the same regime," Mugabe said, referring to Muzorewa's warning to Mozambique and Zambia to stop aiding the guerrillas and the renewed Rhodesian bombing of his camps in northern Tete Province here earlier this week.

"It's the same policy, and I don't think there will be any change," he said. "There cannot be any compromise with [the Muzorewa government.] Negotiations must be between us and Britain," the former colonial power.

Although his comments in an interview with three western journalists followed previously stated policy, timing of them underlined the enormous difficulty Washington and London face in either trying to broaden the Muzorewa government to include the Patriotic Front leaders or to arrange for negotiations between the two sides.

Mugabe warned that if the objective of new British-American proposals was "to marry" the Patriotic Front guerrilla alliance to the new Muzorewa government, he would "of course, not" consider them. Mugabe and Joshua Nkomo lead the Front.

As for allowing Muzorewa to participate in new elections arranged by Britain and the United States, Mugabe said he did not think the bishop could "satisfy the test of eligibility" because of what he called Muzorewa's growing "criminal" record of murdering and hanging Africans.

A special British envoy is scheduled to make a tour of the front-line African states that support the guerrillas and to hold talks with Mozambican officials and Mugabe here June 17.

Mugabe seemed extremely relaxed and confident about the way the war is going and seemed mostly concerned about possible Western military assistance for the Muzorewa government, should President Carter ultimately decide to lift economic sanctions.

Even if Washington were to lift sanctions against the Muzorewa government at some point in the future - which he said would be a "very unfortunate thing" - the crucial question for Mugabe is diplomatic recognition of the Salisbury leadership.

"What matters really is relations," he said. "Will it be possible to have harmonious relations with the United States and Britain? These are the questions that Britain and the United States must answer now."

In any case, he said, recognition would not bascially alter the prospects for the military defeat of the new black-led government in Salibury.

"This would only lengthen our struggle but not affect our strategy to achieve (military) victory," he said.

"Our position is very strong," he added, asserting that it was "within our power" to keep lines of communication disrupted inside Zimbabwe-Rhodesia.

He said his Zimbabwe African National Union had so far fully "liberated" one-third of the country,, "semi-liberated" another third and controlled 1.3 to 1.5 million of the country's total 6.8 million blacks.

He dismissed as totally ineffectual the current Zimbabwe-Rhodesian policy of arming thousands of African "auxiliaries" loyal to the bishop as a way of combating the guerrila forces.

"Fortunately this has also meant arming us," he said."Quite a lot of materiel has come our way."

Explaining for the first time details of the unity agreement he reached in talks May 10-12 with Nkomo, Mugabe said it provided for the Front to be led by a 12-man Coordinating Council and an eight-member Defense Council with each side providing half the number. He and Nkomo would take turns heading the coordinating body, each serving as chairman for a month at a time while the other would lead the Defense Council.

A proposed Joint Operations Command still had to be constituted, he said.

"I shouldn't pretend this is the best possible," he said.

"But there is a far better understanding then there was before and the opportunity has been created for greater military cooperation."

The two rival guerrila factions of the Front agreed to unite their military units for attacks on selected targets inside Zimbabwe-Rhodesia and agreed to try to train together again, he said. There would not be, however, total military integration of the two forces as he had hoped, he added.

Both Mkomo and Mugabe have been under mounting pressure from the front-line states, Cuba and the Soviet Union to unite their political parties and military forces in one body.