The Zimbabwe African National Union, the Mozambique-based wing of the Rhodesian nationalist Patriotic Front, formally rejected any further participation by the United States in negotiations for a settlement of the Rhodesian dispute yesterday.

In a statement issued by its central committee, the militant ZANU faction of the guerrilla front said that by permitting Rhodesian Prime Minister Ian Smith to visit the United States, Washington had exceeded its role as a mediator and should be excluded from all conference about Rhodesia.

ZANU's action is a blow to the Carter administration's diplomacy in southern Africa generally and in Rhodesia in particular.

It is bound to make any future joint British-American initiative regarding Rhodesia extremely difficult and will leave London on its own to find a way out of the current impasse over convening a conference of all parties to the Rhodesian dispute.

"We are now compelled to state that all future conferences on Rhodesia, the United States government participation be excluded," the ZANU statement said. "They have by admitting Smith and his gang exceeded their jurisdiction as mediator."

It continued that while the United States as a sovereign state is free to admit whomever it pleases, it is similarly ZANU's right to demand that states who have no legal right or interest in the Rhodesian constitional situation ought not to have any presence at any future constitutional conferences dealing with this matter. "We now name the United States as one such state which must never attend."

The statement was issued only in the name of ZANU, the Chinese backed Rhodesian nationalist faction led by Robert Mugabe. There was no indication that ZANU had consulted with the Zambia-based wing of the Front, the Zimbabwe African People's Union (ZAPU) headed by Joshua Nkomo.

Nkomo, for his part, has already said that the all-parties conference promoted by Britain and the United States is "dead and buried" but has not yet excluded future American involvement in the negotiations over Rhodesia.

The ZANU statement said the United States has been losing interest in the British-American proposals for a settlement in Rhodesia since the conference involving the two Western powers and the Patriotic Front in Dares Salaam, Tanzania, last spring.

Smith and the three moderate black leaders of the present Rhodesian transitional government refused to attend the Dar es Salaam meetings, which ended in failure.

ZANU traced what it called American "Equivocation" in Rhodesia to the internal settlement reached between Smith and the three black leaders - Bishop Abel Muzorewa the Rev. Ndabaningi Sithole and Chief Jeremiah Chirau - last March, and indicated that it believes the United States is looking for ways to save the multiracial transitional government set up under that accord.

The statement showed no appreciation of President Carter's refusal to see Smith on his current American visit and ignored the administration's refusal so far to give open support to the interim government.

"Throughout our long and arduous struggle for national liberation and independence," the statement said, "The United States as captain of world imperialism has consistently resisted and opposed our people's just demands."

ZANU leader Mugabe had indicated in an interview Sunday that the administration's decision to allow Smith into the United States was a turning point in his group's attitude toward Washington's role.

"We don't have to negotiate with the United States," he said. "The only colonial power is Britain. If the United States is now actually subverting us and suddenly introducing the issue of legal recognition of the internal (Rhodesian) regime, then in our opinion it has exceeded the limits of the jurisdiction we have allowed it."

Mugabe's thinking was strongly reflected in the central committee statement issued from its headquarters here after four days of debate within the organization.

Meanwhile, ZANU also called upon Zambia yesterday to review its decision to partially open its border with Rhodesia to make use of that country's rail link with South Africa to get its exports out and imports in.

It said Zambian use of the Rhodesian railway would create a new source of renevue for Rhodesia, provide it with much-needed foreign currency and help to strengthen its shaky economy. "Our fighting strategy has been directed at the destruction of his economic strength," the statement said.

ZANU appealed to the Organization of African Unity and to the United Nations to come to Zambia's rescue with emergency measures to help it meet is economic crisis, uphold U.S. sanctions against Rhodesia, and "Avoid actions whose effect is to negate the progress in our war effort."

Meanwhile, Reuter reported from Salisbury:

Muzorewa left to join Smith and Sithole in the United States yesterday after issuing an appeal to guerrilla leaders to return home and work for peace. In a statement, he asked Mugabe and Nkomo to take heed of this week's announcement by the transitional government that all racial discrimination in Rhodesia is to be abolished.

Urging them to return home he said: "I believe that enough success has been achieved to turn the tide of events from war to peace. Those of our beyond children who fought for change must honestly accept that the desired change has been achieved."

He said the guerrillas are now fighting "a war already won, bringing needless death to our innocent population."