President Carter yesterday moderated the statement of National Security Affairs Adviser Zbigniew Brzezinski on Wednesday tying the fate of the strategic arms limitation talks (SALT) to the Soviet Union's military activities in the Horn of Africa.

If there is such a link, Carter told a nationally televised news conference, it is because the Soviet role in that part of the world is bound to affect American public opinion in the Senate, which would have to approve any new SALT accord.

Brzezinski suggested to reporters on Wednesday that continued Soviet and Cuban military support for Ethiopia in its fighting with Somalia could make it more difficult even to reach a new SALT agreement.

Carter yesterday steered clear of that notion, saying there was no administration policy tying the two together.

But he added that if the Soviets persist in a military role in the Horn of Africa it "would lessen the confidence of the American people in the world and peaceful intentions of the Soviet Union, would make it more difficult to ratify a SALT agreement or comprehensive [nuclear] test ban agreement if concluded, and therefore, the two are linked because of actions by the Soviets.

"We don't initiate the linkage," he said.

In his comments, Brzezinski noted the likely impact of the Soviet role in the Horn of Africa on Senate consideration of a SALT treaty. But he took it beyond that point that Carter also made yesterday by suggesting that the Soviet activities would "inevitably complicate . . . the negotiating process itself . . ."

The Carter administration has always officially rejected the concept of "linkage," under which the U.S. attitude toward negotiations with the Soviets would be linked to Soviet actions around the world. At the same time, the administration is attempting to focus increased public attention on the conflict in the Horn of Africa and the Soviet and Cuban role in the fighting.

The State Department estimates that there are about 1,000 Soviet military advisers and more than 10,000 Cuban troops in Ethiopia, which is fighting somalia over control of the Ogaden region, an area of Ethiopia largely populated by ethnic Somalis.

The United States has called for Somalia to withdraw its troops from the region and has received assurances from Ethiopia and Soviet officials that Ethiopian forces will not invade Somalia.

On another foreign policy topic at the news conference, the president strongly reiterated his support for the withdrawal of Israeli forces from occupied Arab territories as part of a Middle East peace settlement. That issue is likely to be a key subject in Carter's discussions later this month in Washington with Israeli Prime Minister Menachem Begin.

"One of the crucial elements of any progress in the Middle East is a cleaving to the commitment that U.N. resolution) 242 is a basis for continued negotiations and a solution," he said. "The abandonment of that would put us back many months or years. So this is what I hope to accomplish with Prime Minister Begin . . ."

United Nations resolution 242, adopted in 1967, calls for Israeli withdrawal "from occupied territories," In recent weeks Begin has hinted he does not consider the resolution applicable to the occupied territory on the West Bank of the Jordan River.

The news conference was held at the National Press Club and, in keeping with the club's practice, questions were submitted to Carter in writing.

Immediately before the news conference, the present delivered a brief speech outlining his civil service revision proposals he sent to Congress yesterday.

Asked about the decline of his standing in the public opinion polls, Carter said, "I might say we have had to deal, and have decided to deal, with some longstanding, very difficult, controversial issues that in some instances had not been adequately addressed by my predecessors."

The president claimed for himself "remarkable success" in reducing unemployment and inflation and noted that "the polls show that my own personal popularity is very high."

"We are making good progress and I am not disappointed at the progress that we have made," he said.