President Carter announced yesterday that he will maintain economic sanctions against Zimbabwe-Rhodesia for the present, but suggested that he might change his decision if the new biracial government there makes progress toward "genuine majority rule."

In a vigourously worded statement that he personally read to reporters at the White House, the president stressed that he was acting not only to promote racial justice but also to protect U.S. national interests. He said his decision would maintain good diplomatic and economic ties with black Africa and limit outside exploitation of southern Africa's racial crisis.

"I intend to do everything I can within my power to prevail on the decision," the president said in acknowledging that he faces an uphill battle in keeping Congress from overriding his ruling on sanctions immediately.

"It means a lot to our country to do what is right, what is decent, what is fair," he said.

But Carter coupled this with measured praise for recent "encouraging progress" in Zimbabwe-Rhodesia, where April elections brought to power a biracial government headed by Prime Minister Bishop Abel Muzorewa. Carter said he will consult with Congress once a month on the amount of progress being made by Muzorewa toward "genuine majority rule."

Carter and Secretary of State Cyrus R. Vance, who answered reporters' questions after the president spoke, refused to spell out what actions Muzorewa would have to take to get the president to change his decision.

But both the praise and the implicit suggestion of a possible change in the sanctions decision in the future represented a clear shift from the administration's previous strong alignment with key black african states that unreservedly condemned Muzorewa and that still insist that internationally supervised elections and a negotiated settlement to the country's guerilla war must precede an end to sanctions.

The decision announced by the president represented a compromise that involved "keeping sanctions on while telling Muzorewa that he did not have to go all the way back to square one," said one administration official involved in the lengthy review that led to yesterday's announcement by Carter.

As part of the new effort the administration will dispatch a special diplomatic representative to Salisbury periodically to monitor Muzorewa's progress toward "broader political participation," Vance said.

Carter's statement appeared to rally congressional supporters of the administration's Africa policy, but the conciliatory balancing remarks were immediately spurned by Muzorewa in Salisbury and by Senate opponents who will reopen their campaign to end the trade embargo on Monday.

Muzorewa, the African nationalist who replaced white settler Ian Smith as Zimbabwe-Rhodesia's prime minister earlier this month, called Carter's action "an inhuman decision." Sen. S. I. Hayakawa (R-Calif.) called it "a non-decision, a Hamlet-like to-be-or-not-to-be decision. I am afraid it will lead to disaster."

Sen. Richard S. Schweiker (R.-Pa.) called Carter's action "a slap in the face to the U.S. Senate," which voted 75 to 19 last month for a resolution offered by Schweiker expressing support for the immediate lifting of sanctions.

Carter and Vance met with the Senate and House foreign affairs committees just before making the announcement of the determination. Sen. Jesse A. Helms (R-N.C.) asked Carter at the meeting to invite Muzorewa to Washington for direct talks, and said later that Carter did not rule out the idea.

At the center of the continuing dispute over sanctions are the parliamentary elections held in Zimbabwe-Rhodesia in April, in which a government-estimated 63 percent of the country's 8 million people voted.

Under 1978 legislation Carter was required to end the trade embargo if he determined that a government had been installed in the breakaway British colony by free and fair elections. Secondly, that government had to make a genuine effort to negotiate an end to the guerilla war being fought against the Salisbury government by the Patriotic Front.

Carter said yesterday that "the actual voting" in April has been conducted in "a reasonably fair way under the circumstances," but then went on to rule that the elections were not "either free or fair" primarily because of the constituion under which they were held and the restrictions placed on political activity by the Patriotic Front.

He noted that the constitution had been approved only by the country's 4 percent white minority, and had never been voted on by the 96 percent black majority. The constitution reserves control of the army, policy and justice system to the whites, and the whites' "vastly disproportionate vote" in parliament gives the white minority "a veto over any significant reform" in the constitution.

Carter also pointed out that the political representatives of the Patriotic Front organizations based inside Zimbabwe-Rhodesia had been banned for participating in the election campaign.

Finally, he said, while Muzorewa had offered to attend an all-parties conference with Patriotic Front leaders Robert Mugabe and Joshua Nkomo, the new government in Salisbury had not yet indicated a serious willingness "to negotiate all relevant issues" at the 1978 legislation.

But the president went far beyond the legal grounds of his decision to lay heavy and repeated emphasis on his view that lifting sanctions would inflict substantial damage not only on his Africa policy but also on U.S. national interests.

In response to a question, Vance later confirmed that Nigeria had indicated to the United States that lifting sanctions might have an effect on Nigerian oil deliveries to the United States.

Moreover, in a clear reference to the Soviet Union, Carter said keeping sanctions in place would "limit the opportunities of outside powers" to take advantage of the situation in southern Africa at the expense of the United States.

Asserting that he has done "what is right and decent and fair," Carter said his decision was rooted in America's "sense of racial justice."

Carter's open stress on the national interest in his public announcement and at the private meeting with the two congressional panels was praised by Sen. Paul Tsongas (D-Mass.) who predicted that Senate liberals "would do much better this time, when many senators will understand that lifting sanctions means writing off black Africa and inviting the Russians to exploit the situation."

Sen. Jacob K. Javits (R-N.Y.), one of the cosponsors of the 1978 legislation that forced Carter's determination yesterday, indicated that he is now prepared to give Carter more time on sanctions. CAPTION: Map, no caption, By Dave Cook - The Washington Post