The Congressional Black Caucus urged President Carter yesterday "to publicly condemn" Rhodesia's internal plan for black majority rule because it excludes the leaders of guerrilla forces fighting Prime Minister Ian Smith's government.

Shortly afterward, Carter said at a press conference that he doubted there could be a settlement "without including a right for all the nationalist leaders to participate."

These leaders, he said specifically, inclue Joshua Nkomo and Robert Mugabe, who head the black nationalist Patriotic Front combating Smith's white-minority regime from bases in Mozambique and Zambia.

The president's comment was basically a restatement of positions already enunciated by the administration and was not made in direct response to the appeal from the 16 Congressional Black Caucus members.

But, it did appear to mirror increasing concern within the administration that the Rhodesia problem could trigger domestic political repercussions. Specifically, this fear is that U.S. efforts to promote a peaceful Rhodesia settlement could get caught in a crossfire between congressional supporters of the Smith plan and American blacks who consider it inadequate.

At issue is the so-called "internal solution" signed in Aalibury las week by Smith and three black leaders to bring majority rule for the African nation 6.7 million black and 263,000 whites. It would make Smith and three black ministers the central authority until elections for a new government on Dec. 31.

However, the Patriotic Front leaders have rejected the plan as a "fake" designed to propagate white rule. In the face of that split, Washington's approach has been to try and straddle the dispute whil seeking a compromise acceptable to the feuding black nationalist factions.

Following a strategy meeting here Wednesday between Secretary of State Cyrus R. Vance and British Foreign Secretary David Owen, Vance said the Salisbury agreement, while a "a significant steps," must be greatly clarified and improved if it is to serve as the basis for an acceptable solution.

However, there are increasing signs of domestic U.S. impatience with this administration attempt to play for time. Some conservative and moderate members of Congress, spurred in part by heavy lobbying from mining interests who want access to Rhodesian chrome, have been saying the Washington should consider serious backing the internal solution.

Yesterday, for example, four members of the Senate Foreign Relations Committee - Clifford P. Case (R-N.J.), Jacob K. Javits (R-N.Y.), Richard Stone (D-Fla.) and Chairman John J. Sparkman (D-Ala.) - introduced a resolution saying the Salisbury accord "should have the serious and impartial consideration of the U.S. government" and should "not be rejected out of hand."

A spokeman for Case, principal backer of the resulution, said it was not intended as an endorsement of the internal solution. Instead, he added, it was a plea for the administration to carefully consider all courses that might promotes "a moderate solution."

A different tack was taken, though, by the Black Caucus in an open letter sent to the president by Reps. Parren J. MTchell (D-Md.), the chairman and Charles C. Diggs Jr. (D-Mich.), the caucus' international affairs spokesman. It said that failure to condemn the internal settlement could "make our country accomplics in what could be a protracted black on black war . . ."