Former president Ford said yesterday that President Carter must "take a harder line with the Soviets" and tell them that "if they persist in their adventurism . . . in Africa," a new strategic arms treaty "is not a possibility."

Ford, who launched the diplomatic effort for a broader Strategic Arms Limitation Talks (SALT) pact with the Soviets during his two years in office, said he "would not rule out" using the SALT discussions in an effort to slow down Soviet and Cuban involvement in Africa.

"As strongly as I feel a good SALT II agreement is in our national interest," he told a press conference at the American Enterprise Institute, "I would not rule that out."

Ford's comments came just two days before his successor is scheduled to meet with Soviet Foreign Minister Andrei Gromyko to try to clear up the few remaining disagreements on a new SALT pact.

Carter has sought to avoid what he calls "linkage" between the arms talks and Soviet actions in Africa - a subject of increased public and private concern to the administration. Ford said he, too, wanted to avoid the word "linkage," but said there had to be "an interrelationship" between the two issues. He said it was "incredible" to suggest that the United States had no way to exert pressure on the Soviets or Cubans to reduce their intervention in African countries.

[Asked at his Chicago news conference yesterday about Ford's remarks, Carter said he thought Ford's "analysis is that we ought not necessarily to let Soviet action in other areas interfere with the progress of SALT. But he pointed out, and I agree, that unless the Soviets do honor the constraints on basic human rights, unless they also honor constraints on their involvement in places like Africa, that it will have a strong adverse effect on our country and make it much more difficult to sell to the American people and to have ratification in Congress of a SALT agreement should it be negotiated . . .]

["So I never have favored the establishment by me or Brezhnev of a linkage between the two, so that, if the Soviets and the Cubans stay in Ethiopia, for instance, we would cancel the SALT talks. I think that the SALT agreement is so important for our country, for the safety of the entire world, that we ought not to let any impediment come between us and the reaching of a successful agreement. "But there is no doubt that if the Soviets continue to abuse human rights, to punish people who are monitoring the Soviets compliance with the Helsinki agreement, which they signed on their own free will, and unless they show some constraints on their own involvement in Africa and on their sending Cuban troops to be involved in Africa, it will make it much more difficult to conclude a SALT agreement and to have it ratified once it is written."]

In a question-and-answer session studded with sharp criticisms of Carter's economic and foreign policy actions, the former president endorsed his successor's plea for greater freedom from congressional constraint in the conduct of international affairs.

"I have said repeatedly and emphatically that Congress has encroached much too far on the prerogatives of the commander in chief . . . to conduct foreign policy," Ford said.

"I hope that Congress will back off and give the president a freer hand to do what is right . . .," he said.

Carter has complained publicly in recent weeks of legislative restrictions on aid to African countries facing communist-backed military threats. Members of his administration have explored the possibility of lifting bans on military aid to one of those countries, Angola.

Ford recalled that he had tried to aid Angola when he was in the White House and had been blocked by Congress - a step he blamed for the victory of the Soviet-backed forces.

More recently, he said, the Carter administrations "mistake is not supporting an internal settlement in Rhodesia has whetted the appetite of the Cubans and the Soviet Union" for a proxy-takeover of that country.

On the domestic front, Ford labeled Carter's fiscal policies "a disaster" and said the Democratic administration "will have to take responsibility" for the resurgence of inflation he blamed on higher federal spending.

Despite the sharpness of his criticism of his successor. Ford remained noncommittal about his interest in a possible rematch with Carter in 1980, saying he would not make that decision for the next 12 to 18 months.

Asked about a Louis Harris-ABC News poll that showed him leading Carter, 48 to 43 percent, in a trial heat, Ford said, "I have a lot of time and there will be a lot of polls . . . We'll just wait and see."