At the most sensitive time for shaping American-Soviet relations since President Carter took office, the signs of internal division among his administration's foreign policy managers are becoming increasingly visible.

Until last week, the administration generally was able to keep its differences over foreign policy out of public sight. Even the highly publicized utterances of "point man" Andrew Young, ambassador to the United Nations, helped to reinforce the image that everyone else at the top was in step with the "collegial approach."

The discord displayed last week punctured that claim. It revealed a dispute that extended through the top layer of the foreign policy establishment, not on a marginal issue, but on the core subject of detente strategy.

The administration's ill-coordinated public attempt to try to moderate Soviet policy in the Horn of Africa by tying it to the American-Soviet strategic arms limitation talks (SALT) went badly awry.

Instead of focusing attention on the need to halt and reverse the flow of Soviet and Cuban forces to Ethiopia in its war with Somalia, the effort drew attention to disagreement inside the administration on its Soviet strategy.

President Carter and national security adviser Zbigniew Brzezinski, and Secretary of State Cyrus R. Vance and chief SALT negotiator Paul C. Watnke, appeared openly at odds on whether there is "linkage" between the Horn of Africa and SALT.

Despite the official U.S. claim that the Carter administration was not "imposing" linkage but only pointing to the inevitable political "spillover" consequences of Soviet actions, the Soviet press denounced the whole affair as attempted "blackmail."

The diplomatic consequences, officials ruefully conceded in private, was that American strategy was characterized as "totally confused." Many officials expressed hope that the "linkage" dispute would quickly disappear.

Brzezinski's public stress on "linkage" was privately derided by State Department critics as "about as effective as shooting yourself in the foot."

But Brzezinski was by no means alone in dramatizing the linkage issue. He seemed to have an ally in President Carter. While avoiding a total endorsement of Brzezinski's position on Africa-SALT linkage, Carter publicly came out closer to what Brzezinski said than he did to the position expressed by Vance and Warnke.

The Unites States previously said it was suspending American-Soviet talks on arms limitation in the Indian Ocean because of Soviet actions in the Horn of Africa. This was a calibrated "signal" of displeasure with Moscow. In addition, visiting Soviet parliamentary delegation last month was cautioned -- in private -- by the president, State Department officials and by numerous members of Congress about possible jeopardy to broad U.S. Soviet interests, including the nuclear negotiations.

President Carter then decided, at a National Security Council meeting, to increase the public display of concern. A State Department source protested last week that "instead of turning it up a notch, as intended, Brzezinski turned it up five or six notches."

The dominant question is whether Brzezinski, or Vance, is closer to the president's overall intentions. On Friday the White House openly criticized the Soviet position on human rights in a communique that concluded the East-West conference in Belgrade on European security and cooperation; a senior State Department official, the day before, said it was unrealistic to expect more from the Soviets in the communique. State officials tried to swallow their chagrin.

High attention is now centered on National Security Council meetings this week and beyond, where decisions will be made on the next stage of the nuclear negotiations in Geneva.

There is great speculation about whether the linkage issue will dissolve or disappear in the secret instructions that Carter sends to the American SALT delegation.

Many insiders and outsiders are convinced that the president already has decided not to try for a SALT agreement this congressional election year, because of the controversy it would provoke on top of the Panama Canal treaties debate. Numerous politically vulnerable congressmen have urged the White House to delay on SALT.

Even if ratification of a SALT pact is beyond reach this year, its champions (many of whom refuse to concede that) urge the completion of negotiations as rapidly as possible. Otherwise, they warn, there is the risk of a political shift of power in Moscow, plus a critical risk of lost momentum through delay, which can make the current negotiating pattern moot, overtaken by new nuclear weapons development and new commitments to the arms race.

The latter is the president's public position.

Carter sent Warnke back to Geneva with newly pledged support to try to bring the prolonged nuclear negotiations to a successful conclusion this year. That may require, the president said Friday, a meeting with Soviet leader Leonid I. Brezhnev, to resolve several "quite significant" obstacles.

But there are basic divisions, officials are now more prepared than ever to admit in private, about how toughly, or how moderately, the United States should conduct its end of the zig zag policy of competition and cooperation with its principal world adversary.

This is "a spectrum of opinion -- not a split," some senior officials insist. However, no matter how it is described, it amounts to a continuing contest for influencing "the president's mind." And there is increasing talk among Senior officials of "the absence of consistent presidential leadership."

Carter came into office describing himself as an "eager student" of former professor Brzezinski. From the outset, Brzezinski has publicly stressed that the Soviet Union must be induced to make American-Soviet detente "more reciprocal."

This means, Brzezinkski has emphasized, "that the rules of the game are the same for both parties."

In Brzezinski's perception, the United States must not shrink from allowing the competitive side of the relationship to surface with stark reality. As national security adviser, he regards it as his special responsibility to bring the "worst case" interpretation of any issue to the president's attention, vigorously.

Vance, and the officials associated with him, including Warnke, and Vance's special adviser on Soviet affairs, Marshall D. Shulman, seek to avoid the polarization of American-Soviet differences.

Brzezinski and Shulman both were professors at Columbia University, representing contrasting approaches to Soviet policy. They remain on friendly and cooperative terms, as do Vance and Brzezinski, who are in continuing, close communication.

Vance, modest, self-effacing and far less forceful than Brzezinski, works quietly to resolve problems by methodically dealing with their components -- the opposite of linkage.

It was Vance, at the outset of the Carter, administration, who publicly renounced the concept of American-soviet linkage pursued intensively by Henry Kissinger in the Nixon administration.

Linkage in 1969 was imposed as policy over the objections of Secretary of State William P. Rogers (like Vance, a lawyer), who was overrun and later succeeded by Kissinger.

With no all-powerful Kissinger to dominate foreign policy below the presidential level in the Carter administration, equal interplay among advisers is more constant, with the president the total decider and chief articulator of policy. Influence of the advisers can shift from subject to subject, with Vice President Mondale, and now also Carter's chief political adviser, Hamilton Jordan, participants in the weekly foreign policy meetings with Carter, Vance and Brzezinski.

Defense Secretary Harold Brown, a negotiator of the original SALT agreements in 1972, and a strong advocate of a new accord, is a major figure in both subjects involved in the linkage debate. Brown, like Vance, Warnke and Shulman, dismisses the idea of invoking linkage in a Horn of Africa-SALT connection, although he is quite concerned about the Soviet-Cuban presence in Africa, as are all senior advisers.

The record on trying to apply "linkage" on SALT is one of failure.

Two years ago, in a memorable exchange in the Kremlin with Brezhnev, Kissinger sought a trade progress toward a new nuclear arms pact for a withdrawal of Soviet-supported Cuban troops from another African nation, Angola.

Before the talks began, Brezhnev was asked by a newsman if Angola would be among the subjects he and Kissinger would discuss, as Kissinger had forecast.

"I have no questions about Angola," responded Brezhnev. "Angola is not my country."

"It will certainly be discussed," quickly interposed Kissinger.

"The agenda," Soviet Foreign Minister Andrel Gromyko said dryly, "is always adopted by mutual agreement."

"Then I will discuss it," Kissinger retorted.

"You'll discuss it with Sonnenfeldt," scoffed Brezhnev, referring to Kissinger aide Helmut Sonnenfeldt. "That will insure complete agreement," Brezhnev gibed, because "I've never seen him (Kissinger) have a disagreement with Sonnenfeldt."

Kissinger told reporters later, "I knew I had no bargaining cards."

A nuclear accord is negotiable only if it provides "mutual benefit,' and Kissinger generally exempted it from the linkage concept, for it offered no ready bargaining on "rewards and penalties."

The "penalty" can only be the general deterioration of detente. Kissinger, later in 1976, warned that would happen; U.S.-Soviet detente, he said, could not survive "another Angola."

It did, but with heavy damage. Soviet-supported Cuban troops are still in Angola in great strength raising a continuing concern for official American policy that is now greatly intensified by the Soviet-Cuban military presence in Ethiopia.

Although U.S.-Soviet detente was not destroyed in 1976, the political outcry that detente lopsidedly benefited the Kremlin caused President Ford to head off the compromise that Kissinger wanted to make to conclude a SALT II agreement. Ford has said in retrospect that he erred. Some Ford aides maintained, in fact, that had Ford gone along with Kissinger, he might have defeated Carter for the presidency.

Some of the identical political cross-pressures are now weighing on President Carter. Brzezinski has said that new SALT concessions to the Soviet Union could stimulate greater political opposition both to the negotiation and the nuclear arms control accord, now under way, and to its ultimate ratification.

Brzezinski's internal critics do not challenge that possibility. But they are dismayed that Brzezinski openly projected it, on grounds that it supplies a "self-fulfilling prophecy," playing into the hands of SALT's Senate critics, led by Henry M. Jackson (D.-Wash.).

Since his days of thwarting Kissinger on SALT, Jackson has gained a position of broader influence over the administration's overall legislative goals. In addition to heading the Senate Armed Services arms control subcommittee, he is chairman of the Senate Energy Committee, handling Carter's most important and elusive domestic priority, energy legislation.

That gives him double checkmating influence now over what is even proposed in nuclear negotiations, and other relationships with the Soviet Union.

Jackson's aides scoff at the "linkage" attempt on SALT. They are out to block any foreseeable administration moves on SALT as "too soft," and maintain that the White House knows that, in any event, ratifying a SALT pact is out for this year.

Senate Majority Leader Robert C. Byrd said over the weekend that he does not "'link' SALT" either. But he forecast a sterner outlook on all cooperation with the Soviet Union, on grounds that its actions in Africa raise "a direct challenge to detente."

This is the broader hazard for Washington and Moscow. The detente relationship has entered another newly precarious stage. It is especially susceptible to new moves that either side may construe as provocative.

There is agreement on that somber assessment across the full spectrum of Carter administration policymakers. What they cannot anticipate with great confidence is what Carter will do. One official wryly remarked, invoking the Nixon administration style admonition:

"Better watch what we do, more than what we say."