President Carter's Rhodesia policy has suddenly come to resemble a Harold Pinter play, in which silences and pauses convey as much as the words spoken by the British playwright's tense, dread-filled characters.

The president is now trying to project to his conservative critics a new flexibility on the breadaway British colony now known as Zimbabwe-Rhodesia, but without spelling it out in words that might assauge the critics but would damage his carefully constructed Africa policy.

The impresssion of Carter playing Rhodesia by Pinter was the net effect of two pieces of political theater forced on the president Thursday. First, at a private meeting with congressional leaders, and then in an appearance before reporters, he announced that he had decided to keep the U.S. trade embargo against Zimbabwe-Rhodesia in effect.

The president would have preferred not to be there at all. Over the past year, the Anglo-American diplomatic initiative to end the disputed territory's guerrilla war has fallen apart under a wide variety of competing pressures. At the same time, conservatives fighting to lift sanctions have gained the upper hand in the Senate. Carter's White House aides appear to wish that the Rhodesia problem would just go away.

But it won't. Under Ambassador to the United Nations Andrew Young's continued prodding, the Carter administration has stuck to a policy that could be reduced in its simplest terms to doing nothing that would give the white settlers, headed by Ian Smith, and their black associates, headed by Bishop Abel Muzorewa, encouragement to believe that the administration would rescue them from a rising tide of black nationalism that threatens to engulf them.

On Thursday, Carter carefully said nothing that would rule out a changed attitude toward the new government headed by Muzorewa if there were progress toward broader political participation. He also did not raise tha administration's previous insistence that broader political participation should include internationally supervised elections and an all-parties peace conference.

In contrast to the previously tightly drawn administration statements on the conflict, Carter's public statement contained a number of nuances that appeared to be aimed at different constituencies. The tough language on keeping sanctions in place for now appealed to African states and to the liberal and black constituencies Young represents in the administration.

But the statement was also clearly intended to leave an impression that he was now more flexible on the ways in which a settlement that establishes broader black rule may be achieved.

"The presedent was saying that we do realize that we have to work from where the situation is now, not from where it was when we started," one aide said.

In addition to promising to consult on a monthly basis with Congress about the progress Muzorewa is making, the administration is also sending a full-time diplomatic representative to work on Rhodesia. The representative is likely to be a middle-level Foreign Service officer who will be assigned to the U.S. embassy in South Africa, administration officials said yesterday.

Carter may have succeeded in buying some time from congressional critics. One of the key figures in the Senate battle, Sen. Jacob K. Javits (RN.Y.), emerged from the meeting under the impression that Carter would be reviewing sanctions on a month-by-month basis, although the president actually described the review in more general terms.

"It's my judgment that the president is likely to have bipartisan support" for his lastest approach, said Javits, who had been leaning toward an immediate lifting of sanctions. "I believe the president, under the reasons he's given us, is entitled to have people like myself very carefully review his reasons, which are weighty and critical to the national interest."

Underlying the strategic reasons Carter cited in defending his decision is the unspoken assumption that lifting sanctions would steady the Muzorewa-Smith forces enough so they would believe they could get by without making the fundamental changes that would lead to "genuine majority rule."

This in turn would lead to a lengthening of the war, which radicalizes the region more intensely the longer it lasts. The Soviet Union appears to have a policy for Zimbabwe-Rhodesia based on the acceptibility of violent change. Whether the extra time Carter may buy from his congressional critics will enable him to shape a policy to promote non-violent change in Zimbabwe-Rhodesia is as uncertain as a Pinter ending.