Rhodesian guerrilla leader Joshua Nkomo sharply criticized the United States and Britian yesterday for what he termed their wait-and-see reactions to the evolving "internal" plan for Rhodesia's future being worked out in Salisbury.

Visibly furious over the negotiations between Rhodesian Prime Minister Ian Smith and three black nationalist leaders who live in Rhodesia, the coleader of the guerrilla Patriotic Front was most vehement in his comments on British Foreign Minister David Owen.

"He is a racist," Nkomo said. "I'm sorry to say it, but his attitude toward Smith and the Patriotic Front shows that when a white man is in control, he [Owen] sees fairness."

Nkomo's remarks and a sharp denunciation of the Salisbury plan from the Mozambique-based wing of the Front as a "treacherous sellout" amounted to a sharp setback to British and American hopes for eventually merging the "internal" talks and their own "external" negotiations into one overall settlement package.

They seemed to indicate, that London and Washington may well have to choose soon between backing Smith's internal agreement or sticking with their own rival proposals for a settlement involving negotiations with the Front.

Nkomo was uncompromising in his opposition to the Salisbury talks and heaped scorn on the nationalist leaders negotiating with Smith.

"That these black men in Salisbury should have been parties to such an agreement must rank as the greatest sellout in the history of Africa," Nkomo's organization, the Zimbabwe African People's Union, said. Zimbabwe is the African name for Rhodesia.

"Weare going to continue with the armed struggle," Nkomo said, during a press conference at his headquarters here. "We shall intensify it . . . because we believe it is the only way to bring about the required change."

He made it clear that the Front would not allow elections to take place inRhodesia, saying the war would continue and that polling booths would be considered "military targets" of the guerrillas.

There are fears among Western observers here that the guerrillas and the "front-line" states backing them are bracing for a sharp escalation in the war, in Rhodesia, which could then spread into neghboring countries and lead to soviet and Cuban involvement.

The 60-year-old nationalist leader went over the announced terms of the Salisbury agreement point by point and concluded that "it means the status quo is to remain and prevail" for another 12 years at least, "and perhaps indefinitely".

"What Smith has conceded is not majority rule, but one-man, one-vote for the election of 72 powerless seats in parliament, 72 (black) dummies with no power," he said of the proposal for a new National Assembly consisting of 72 seats for blacks and 28 reserved for whites.

"All powers of state remained intact, in the hands of the minority and this is what Dr. Owen calls a step in the right direction and he welcomes it," Nkomo said bitterly.

After the initial Salisbury agreement was announced Wednesday, Owen, who is under pressure from Conservative politicians to back the Smith accord, called it "a significant step toward majority rule."

The initial U.S. reaction to the Salisbury plan, from Ambassador to the U.N. Andrew Young, warned that it could lead to another 'Angola-type situation" in whiich blacks fight blacks in a bloody civil war.

"This is not a settlement addressing itself to the issues for which some 40,000 guerrillas are fighting," Young said.

By Thursday, however, the State Department was more restrained, saying that the settlement "represents only a part of a much larger and more comprehensive set of arrangements," and adding that any further comment would have to await a full text of the Salisbury accord.

Nkomo denounced the entire concept of providing a special position and guarantees for Rhodesia's 263,000 whites as simply "entrenching apartheid" in a constitution. At present Rhodesia's 6.8 million blacks have partically no voice in the government.

"We are not giving our lives for a constitution that is going to entrench the position of the white man. We are fighting for a nonracial state. This alone disqualifies the whole thing," he said. "We cannot be party to a document that enternches discrimination."

The Front leader seemed to find virtually all the terms of the proposed internal agreement unacceptable. He said guarantees for an independent public service and tenure for present jusges and civil servants were tantamount to perpetuating the status quo.

As for the provision blocking any changes in the "entrenched clauses" protecting white minority rights for at least a decade, he said, "This means there will be no change for 10 years," in addition to another two to three years during the transitional period.

He was referring to reports that the Smith government is asking for the proposed interim multiracial government to continue in power for two years or longer.

A simlar analysis of the Salisbury plan came in a statement from the Mozambican capital of Maputo where the other wing of the Patriotic front is located. It said the agreements terms "guarantee that white settlers will remain in possision of our people's stolen land: The judiciary presently comprised of racists and genocidal judges will be preserved (and) the public service will remain all white for the forseeable future."

Both wings of the Front also denounced in bitter and uncompromising language the three black leaders involved in the Salisbury talks: Bishop Abel Muzorewa, the Rev. Ndabaningi Sithole and Chief Jeremiah chirau.

The Maputo wing, the Chinese-influenced Zimbabwe African National Union (BANU) under Robert Mugabe said the "Gang of Four," a references to the three internal nationalist leaders and Smith, "will be smashed."

Inkomo, who is backed by the Soviet Union and Cuba, referred repeatedly to Bishop Muzorewa and Rev. Sithole as "those two men of God." Nkomo said that by their involvement in the Salisbury agreement they were giving their blessing to the present "oppression, the hangings, the killings, the burnings, the detentions without trials, the shootings of young children and women."

The attacks on the three internal black leaders demonstrate just how dep is the divide between the country's black nationalist leaders, making a compromise among them apparently impossible.

United Press International reported from Salisbury:

Smith and the three black leaders met again yesterday in a session in which the black leaders presented a unified proposal for an interim government leading to majority rule, the main element left in the Salisbury negotiations.

Conference sources said the black leaders proposed that Smith's government be replaced by a ruling council, made up of the four groups in the talks and an independent chairman from Rhodesia or abroad. The council would name a council of Ministers to administer policy.

Smith has given no indication, however, that he would step down during the transition period.