The shift in President Carter's human-rights campaign from shrill publicity to quiet diplomacy became evident in one aspect of his talk with Soviet Foreign Minister Andrei Gromyko Sept. 30.

Although strategic arms and a Mideast settlement were the centerpieces, the President pointedly raised one of the most celebrated Soviet human-rights cases, believed here to be a direct violation of the Helsinki accords: the case of Anatoly Scharansky. Scharansky, a leading dissident, was arrested without public charge in mid-March and, so far as any one in the West knows, is still in jail.

Eschewing hints of threat or retaliation (both clearly in the U.S. arsenal). Carter repeated privately what he had said publicly on June 13: that the still unpublished charge of high treason against Scharansky as a U.S. spy is without foundation. He asked Gromyko to convey his strong personal hope to President Leonid Brezhnev that Scharansky be set free.

Carter's new hush-hush approach to human rights, a keystone of his foreign policy, was dramatically different from the soap-box treatment of earlier days, but so was Gromyko's response. He accepted the Carter message without reproach.

This toned-down exchange between the two leaders also contrasted sharply with the ferocious exchange between Rita Hauser, a U.S. delegate, and key Communist Party leaders at the so-called U.S. Soviet "Dartmouth" conference in Riga, Latvia, last July. When Hauser raised the Scharansky case and asked for an explanation, Soviet members of the conference flared, caustically telling her it was not the business or the United States, that it was strictly an "internal" matter and that Soviet legal authorities had "evidence" against Scharansky.

The muted publicity now being given the human-rights campaign has led many critics toward this angry but unproved conclusion: Carter, his White House adviser, Zbigniew Brzezinski, and the State Department, stung by the Kremlin's public fury in expressing displeasure over the U.S. campaign, have backed away from human rights to reach an accommodation with Moscow on strategic arms and other issues.

The critics may prove right in the end, but evidence is lacking today, as witness the following:

Item: In a high-level session with State Department bureaucrats in the National Security Council's situation room the afternoon of Aug. 23, Brzezinski switched signals on U.S. plans for the second session of the post-Helsinki Belgrade conference. In collaboration with Deputy Secretary of State Warren Christopher, he recruited Arthur Goldberg as chief U.S. delegate. Middle-level U.S. diplomats, wanting to minimize U.S. Soviet disagreements, backed Ambassador Albert W.Sherer, a Class 1 career Foreign Service officer who headed the U.S. delegation in last spring's preliminary Belgrade session, but clearly lacks Goldberg's stature.

Item: Goldberg laid down a condition for accepting the post. Although he would not court "confrontation" with the Russians over mind-boggling Soviet violations of "basket three" - outlining basic human rights for nations that signed the 1975 Helsinki accords - he insisted on his unqualified right to "push compliance" by the Soviets.

Item: Pro-human-rights hardliners in the U.S. Commission on Security and Cooperation - set up to police the Helsinki accords - claim that Goldberg's public speeches and private argumentation during closed-door sessions at Belgrade so far are beyond complaint by those wanting the United States to keep Soviet feet to the fire.

Whether this mid-course judgement proves correct by the time the Belgrade Conference ends remains to be seen. One unknown factor is how the Soviets themselves maneuver through the Belgrade conference and deal with pressures from the West to open the human-rights crack wider.

Gromyko's acceptance of Carter's appeal for Scharansky's release without provocative response indicates extreme Soviet wariness the world spotlights the grim human-rights picture in the Communist heartland. Likewise, the Kremlin has suddenly permitted increased Jewish emigrations, which reached more than 1,600 last month - higher than any other month in 1977 (though way below the peak rate of 1973 at the height of detente).

The shift to quiet diplomacy by President Carter has cost him a powerful cutting edge for domestic politics, but quiet diplomacy, as much as the Belgrade conference, may be having a more productive impact on Moscow than the headlines of early 1977. Scharansky still rots in jail, but no formal charge has yet been made against him.