If strategists in Washington and in Moscow are correctly reading each other's diplomatic signals, the United States and the Soviet Union are at their most important crossroad of policy conflict since the Carter administration took office.

Although no single, incipient crisis is at stake, a major stock-taking on the Carter administration is believed to be under way in the Kremlin. The timing is dramatized by the clash of American and Soviet interests in the Horn of Africa. But beyond that flashpoint, the full sweep of the U.S. Soviet detente relationship appears to be up for scrutiny.

Veteran Soviet Ambassador Anatoliy F. Dobrynin left Washington 10 days ago after a series of intensive discussions with Secretary of State Cyrus R. Vance, to give the Kremlin his important, long-range appraisal of where U.S. policy is headed. As it happened the day Dobrynin left, President Carter delivered his strongest warning to the Soviet Union since he has been in office, producing an immediate, bristling response from Moscow.

After Dobrynin departed, another senior U.S. official remarked privately, "I would guess that this is the most difficult return Dobrynin has had since he has been here. It is difficult enough for us to interpret what the administration means."

That may well be an exaggeration on the first count, though not the second. Dobrynin, who is by far the most significant envoy in Washington, has worked through the blackest days for the two nations, starting with the grim Cuban missile crisis of 1962.

Nothing remotely comparable is at risk now. It is not any imminent physical clash that darkens the American-Soviet horizon. Instead, it is the danger of creeping divergence that can intensify polarization in a less spectacular, but more prolonged, pattern than the initial collision between the Carter administration and the Soviet Union over nuclear strategic negotiations in March 1977.

In interviews during the past week, some of the most experienced U.S. diplomats estimated privately that the odds are against a long turn-down-ward in American-Soviet relations. Others were more pessimistic.

All were admittedly guessing, however. "We don't really know what the Soviets think," said one administration planner.

President Carter's stern speech on American defense policy at Wake Forest University on March 17 was "no threat," said this official, and although the Soviet Union "said it means a change in policy, it doesn't."

However, he added, if the Soviet Union thought "we were simply going to roll over" after it "intervened rather massively" in the Ethiopian-Somali conflict in the Horn of Africa, which they say doesn't mean anything [for the detente relationship] [WORD ILLEGIBLE] then they are living in a fool's paradise."

Their reaction to the Wake Forest speech," said this source, "is almost as though it cut too close to the bone."

In addition to the return of Dobrynin for consultations in Moscow, U.S. sources say the Soviet Union has recalled several other diplomats posted abroad, including some assigned to nations in the Horn of Africa region.

Many of the comparatively optimistic current U.S. estimates about the outcome of this policy review are strong influenced by Dobrynin's ability - and assumed desire, which may be another matter - to explain to the Soviet politburo the Carter administration's concept of the competive-cooperative mix in the detente relationship, as Washington intends it to be perceived.

With all of their elaborate communications, the United States and the Soviet Union have a woeful history of miscalculating each other's intenions. Dobrynin is regarded as the most knowledgeable diplomat in the Soviet Union on retrospectively analyzing strategic miscalculations between the two superpowers.

Nevertheless, it is widely recognized in private inside the administration that the most astute analyst in Moscow, or in Washington, can have great difficulty comprehending the diplomatic signals that the Carter administration tries to convey.

"My guess is that the Soviet continue have a serious question mark about the administration," conceded one official, in what some others would regard as a major understatement."It is not as clearly defined for them as the Nixon administration, or even the Ford administration, about our general direction . . .

"They may be confused because there are a lot of voices in this administration. That is unfortunate, but that is a reality, too."

Another policy-shaper, deploring the recent muddled comments about whether the United States would "link" militant Soviet-Cuban actions in the Ethiopian-Somali war to U.S. Soviet negotiations in the strategic arms limitation talks (SALT), was much more blunt:

"I think we have been unbelieveable in our whole handling of 'linkage.'"

After Carter's Winston-Salem speech, which Vance was unable to show Dobrynin when they had lunch the day before, an amplifying message about the speech as given to the Soviet emassy here to be relayed to Dobrynin in Moscow.

Vance's special assistant for Soviet affairs, Marshall D. Shulman, other sources said, urged Dobrynin in the message to examine the total context of the speech, and not simply the portions addressed to the Soviet Union.

At about the same time, White House aides at St. Simons Island, Ga., where the president was spending the weekend, were telling reporters who inquired that Carter's strong words to the Soviet Union about its expansion and use of military power had a dual domestic-international objective.

The White House, aides said, considered the speech crucial to shoring up domestic political support for foreign initiatives. At the same time, President Carter was cautioning the Soviet Union against "an ominious inclination . . . to intervene in local conflicts" with military might had "encouragement for mercenaries" - meaning Cubans.

In the diplomatically significant "linkage" section of the speech, Carter avoided any direct correlation between Soviet actions elsewhere and the SALT negotiations, whose fundamental important he reindorsed.

But in a clear warning that Soviet actions could rebound against U.S. Soviet cooperation "toward common social, scientific and economic goals," he said: if the Soviet Union should "fail to demonstrate restraint in missile programs and other force levels and in the projection of Soviet of other proxy forces into other lands and continents, then popular support in the United States for such cooperation will erode."

This was clearly the most internationally sensitive paragraph in the speech. It was the subject of considerable internal discussion, if not bargaining, before it appeared in final form.

The Winston-Salem speech as a whole has been attributed by some critics to Samuel Huntington of the National Security Council staff, described by one columnist last week as "the last of the hawks."

According to a more senior NSC source, the original speech draft was Huntington's, but it was regarded by presidential national security affairs adviser Zbigniew Brzezinski as "somewhat academic" in tone - too bland.

Brzezinski said in private that it lacked enough "bite." He and deputy David L. Aaron recast portions of it, adding "stiffening." The speech was then reviewed by Vance and Defense Secretary Harold Brown. Vance, who always prefers nonprovocative language, made suggestions for changes, "some of which were accepted," according to another source.

An NSC source said the final language on "linkage" was Vance's - but what it replaced was unspecified. Brown also made some suggestions. The president made his selections from the various advice, and White House chief speech writer James Fallows did the "clean-up" versions.

"There was no real struggle over the speech,"said an NSC source,

When working-level State Department officials read the speech - when everyone else did - "there were a lot of lifted eyebrows," several said afterward.

"The real question was the tone convey what the administration wanted to convey," said one upperlevel State official" . . . It was intended to be a balanced message. . I think the text gave a tone of more harshness than the administration wanted to put into it ."

Interestingly, NSC sources say the reaction they heard from allied diplomats was concern over reports that the speech was intended for "domestic consumption." The inquirers sought, and were given, assurances that it was at least equally intended for foreign ears, as a caution to the Soviet Union.

State Department sources said they heard the opposite reaction, also from allied diplomats: concern that the Carter speech represented a tough shift of U.S. policy on detente. They were told it did not.

Not surprisingly, the Soviet Union gave it the latter, stiff interpretation.

With exceptional speed, Tass, the official Soviet news agency, fired a salvo of alarm over the speech the advantage of an advance text distrib-same day Cater delivered it, with the uted to White House reporters the night before.

The Carter speech, the Tass report said, while reasserting the need for cooperation with the Soviet Union contained "obviously incompatible" elements "which cause apprehension . . ."

Tass said:

"From the essence of the President's speech it follows that the speech it follows that the speech actually means a shift of emphasis in American policy from the earlier proclaimed course towards ensuring national security of the U.S. through negotiations, through limiting the arms race and deepening detente, to a course of threats of threate and buildup tensions."

A tattoo of similar alarms from viet press "commentators" has followed in succeeding days. American specialists have been observing them intently, to see if they exceed the original line laid down by Tass, to signify a conclusive Soviet assessment.

So far, they have not.

In fact, there have been such qualifications as statements that U.S. policy is being "apparently shifted" or that the American purpose "seemed to be to sharpen international tensions."

To U.S. strategists, this indicates that the Soviet debate and analysis of American intentions is continuing.

Many administration planners say they think it probable that the ultimate Soviet decision will be a guarded middle course. That is, to probe further for greater clarification of U.S. intentions, while avoiding grossly arousing new American alarm about venturesome Soviet actions abroad, but without changing the basic course of Soviet behavior in Africa or elsewhere.

This would leave open, among other things, such large questions for U. S. strategists as whether what they sardonically label the Cuban "Afrika Corps" on that continent will be injected into a potential black-black civil war in Africa with Soviet military support.