Suddenly alarmed that the Senate may vote next week to lift the American trade embargo against Rhodesia, the White House ad Senate liberals have launched an intensive last-minute effort to block the move.

Feeding the new concern are reports that conservative senators may trade off their votes on another key foreign policy test next week, the proposed lifting of the arms embargo against Turkey, in return for votes for resuming trade with Rhodesia.

Administration strategists are also concerned about the impact of a continuing visit to Washington by Bishop Abel Muzorewa is scheduled to meet Henry A. Kissinger, the former secretary of state, Tuesday in an effort to get Kissinger's endorsement for the agreement that brought Muzorewa and two other African leaders into a ruling council with Rhodesian Prime Minister Ian Smith.

The battle is over an amendment to be offered by Sen. Jess A. Helms (R-N.C.) to the foreign security assistant bill, which will also carry an amendment seeking the repeal of the arms embargo imposed against Turkey because of the 1974 Cyprus invasion. Staff aides say Helms is not yet committed on the Turkey issue, but he is reported to be ready to vote against lifting the embargo in return for support for his amendment on Rhodesia.

The effect of that amendment would be to end American observance of U.N.-imposed trade sanctions against the rebel British colony for the rest of the year. A slightly different Helms amendment, liftig sanctions for 15 months, picked up 42 votes in the Senate last month in a losing effort, and administration officials concede that the North Carolina Republican has picked up more votes since then.

While House press secretary Jody Powell read a statement to reporters yesterday announcing President Carter's concern about the impending vote. Observing U.N. sanctions has enabled the United States to make "significant advances" in dealing with Africa that would be overturned if the Helms amendment were passed,he said.

Passage "would erode what chances there are for a peaceful settlement, promote chaos and increased bloodshed and pave the way for increased involvement by the Soviet Union and Cuba," Powell said.

That message was also repeatedly stressed during a two-hour presentation at the White House Thursday at which National Security Council and State Department officials briefed 100 Senate staffers, warning that immense damage would be done to American prestige and credibility in the Third World if the Helms amendment passes.

The tone of the briefing was uncompromising, according to Senate staffers present, but other Senate sources suggested that the administration may lean to a compromise amendment if the head count appears to be as close when the vote comes, probably Tuesday, as it does now.

One possibility will be a substitute amendment to be offered by Sens. Clifford P. Case (R-N.J) and Jacob K. Javits (R-N.Y.), who propose to delay the lifting of the embargo until "free and fair" elections produce a government able to show that it will negotiate at a conference with all parties.

The administration continues to support a settlement that would bring together the Smith-Muzorewa government and the guerrilla forces of the Patriotic Front, now fighting a rapidly escalating war against the Salisbury government.

Concern also appeared to be rising sharply in the American black community that the Helms amendment may pass. Trans-Africa, a recently formed lobbying organization, circulated an appeal by more than 30 prominent black leaders, including Los Angeles Mayor Tom Bradley and Mayor Richard Hatcher of Gary, Ind., asking the Senate to reject the amendment.