The title of "ambassador" is essentially misleading when applied to Anatoliy Dobrynin, who finally is leaving Washington after 24 years as the Soviet envoy, for the comparatively unfamiliar setting of the powerful Communist Party secretariat in Moscow.

Dobrynin has been a major participant in shaping and carrying out U.S.-Soviet policy during the Kennedy, Johnson, Nixon, Ford, Carter and Reagan administrations. Dobrynin's role was so exceptional that the Reagan administration, on taking office, made a public point of cutting it back to normal ambassadorial level in perquisites and substance, to underscore a tougher and stiffer relationship with the Soviet Union.

At 66, Dobrynin takes back to the Soviet system a knowledge of the inner workings of the U.S. system that few Americans can match.

The U.S.-Soviet detente of the 1970s was Dobrynin's peak of personal satisfaction and accomplishment. The working relationship that he enjoyed with Henry A. Kissinger, President Nixon's national security adviser, was extraordinary.

In his memoirs, Kissinger said: "The most sensitive business in U.S.-Soviet relations came to be handled between Dobrynin and me . . . . We would, informally, clarify the basic purposes of our governments and when our talks gave hope of specific agreements, the subject was moved to conventional diplomatic channels . . . . Dobrynin was admirably suited to this delicate role."

On the Washington diplomatic, political and social scene, Dobrynin's access to the most influential circles became legendary, as did his cultured affability, sense of humor and ease of manner. But he also was constantly serving Soviet interests. As Kissinger also noted:

"He knew how to talk to Americans in a way brilliantly attuned to their preconceptions. He . . . was especially skilled at evoking the inexhaustible American sense of guilt, by persistently but pleasantly hammering home the impression that every deadlock was our fault."

The collapse of detente, combined with the Soviet invasion of Afghanistan at the end of 1979, was a grievous blow to Dobrynin, even though detente had begun cracking years earlier.

A second blow was the even colder chill in U.S.-Soviet relations that came with the arrival of the Reagan administration. A third blow was President Reagan's Strategic Defense Initiative, also called "Star Wars," which aspires to overturn the concept of nuclear arms control that has evolved since the 1960s.

In a notable departure from his celebrated aplomb and his standard avoidance of strident Moscow-style rhetoric, Dobrynin occasionally has publicly assailed Star Wars as the route to an endless arms race. Speaking in Atlanta last year, he said that during the past five years "we have seen just how stubborn the legacy of the Cold War is."

Dobrynin has abundant knowledge of that period: In his first year as ambassador he received the first ultimatum of the nuclear age, handed to him by Secretary of State Dean Rusk at the peak of the Cuban missile crisis in October 1962.

The American demand for removal of Soviet nuclear missiles from the Caribbean island followed a meeting between President Kennedy and Soviet Foreign Minister Andrei Gromyko, with Dobrynin present. Gromyko told Kennedy there were no Soviet missiles in Cuba for offensive purposes, and Dobrynin said later he had not known that the missiles were there.

American officials debated afterward, inconclusively, whether Dobrynin was uninformed or was lying -- which would hardly be unprecedented in diplomacy. In either case, the official Soviet contention is that the missiles that it was compelled to remove from Cuba were for "defensive" purposes.

The next year brought the first significant turn toward relaxation of tension, later called detente: the 1963 treaty banning above-ground nuclear testing. Dobrynin has been involved in every sequence of thaw or tension in U.S.-Soviet relations, through the Vietnam war to conflicts in the Middle East, Africa and elsewhere.

On many occasions he has worked behind the scenes, with Democratic and Republican administrations -- including the Reagan administration -- to defuse potential collisions between the two superpowers that did not become public. This brought him into unusual personal contact with all American presidents, as well as secretaries of state and national security advisers, over two decades.

In between, Dobrynin and his wife Irina have played host to the top strata of American officials, members of Congress and business and cultural leaders, with some friendships dating back to his first Washington experience, which began as a Soviet Embassy counselor in 1952.

In 1979 his ambassadorial seniority made him, reluctantly, dean of the foreign diplomatic corps, with a stream of ceremonial duties.

To many Americans, Dobrynin is "a charmer," resembling a midwestern banker, with his tall, portly figure topped by a fringe of white hair and gold-rimmed glasses. He also is extremely calculating, and can readily dissemble -- especially about the health of the decrepit Soviet leaders who preceded Mikhail Gorbachev.

The declared reason why the Reagan administration cut back Dobrynin's access in Washington -- first by denying him his unnoticeable entry to the secretary of state's office from the private elevator in the department's garage -- was to raise the stature of the often-sidestepped U.S. ambassador to Moscow.

Outwardly, Dobrynin joked about it. Despite more limited relations with the Reagan administration, he has remained on cordial terms with its officials, notably with Secretary of State George P. Shultz, who shared Dobrynin's desire for improving U.S.-Soviet relations.

The summit meeting last November between Reagan and Gorbachev was the high point for Dobrynin's hopes of the last six years. With their second summit now clouded by uncertainty, however, Dobrynin, as an influential secretary in the party Secretariat, will not be free of his old problems.