Shortly after he became Soviet premier in 1964, Alexei Kosygin went to visit a fisheries plant near Pitsunda, on the Black Sea. The gatekeeper, unfamiliar with his face, refused to admit him without approval by local authorities.

Something like that never would have happened to Stalin or Nikita Khrushchev. But the courtly, self-effacing Kosygin was different from these men, two of his most famous predecessors. He was less impulsive and tyrannical, more pragmatic and better educated. Over the years, his image as a moderate, reasonable and intelligent man gained him greater prestige than any of his colleagues enjoys among the Soviet people.

Few men have stayed in power so long and yet remained so little known. It was perhaps his low-key style that made him seem the "voice of reason" in the Kremlin. But there was something deeper as well. His political career coincided with a distinct phase in Soviet political development in which Stalin's terror and Khrushchev's absolutism had given way to a more orderly system of government.

Soviet observers have frequently argued that Kosygin was the principal sponsor of these changes in the ruling Politburo that during his long tenure -- he became a full Politburo member in 1948 -- has changed from a small group of Bolshevik conspirators to today's board of directors in which various national and other interests are represented.

His resignation yesterday is likely to be seen as having brought about a shift in the Politburo's balance. But, from another angle, his departure symbolizes the new style in Moscow. Khrushchev was the first ruler of Russia not either to die in office or be killed. Kosygin is the first Soviet leader to resign voluntarily. He has been gravely ill for some time.

A dour man of few words, Kosygin sounded more like a Western corporation president than a Soviet politician. A year after becoming premier, Kosygin pushed a series of pragmatic reforms to revitalize the Soviet economy and help it break out of technological stagnation. This has been his main preoccupation for years, according to those who knew him.

But by the late 1960s, it became clear that his reforms were being sabotaged by both the party hierarchy and central ministires unwilling to relinquish power to industrial managers. Another more limited reform attempt was later sponsored by Brezhnev, also without success.

The failure of his reforms had prompted Kosygin to attack the problem from a different angle. He began to emphasize the need for "scientific-technological" changes and established a series of high-powered institutes to promote it.

A textile engineer by background, Kosygin was a director of a factory in Leningrad before he became the city's mayor in 1938. The next year he became minister of textile industry and in 1940, when he was 36 years old, he was promoted to the post of deputy premier. He has remained at the top of Kremlin hierarchy ever since.

In 1948, he was the first technocrat to become a full member of the Politburo, the "baby" among crusty Bolshevik revolutionaries whose sole preparation for power was their clandestine underground activity before 1917.

Steadily gaining authority, Kosygin reached the peak after the fall of Khrushchev in 1964 when he and party leader Brezhnev divided the two key positions held simultaneously by Khrushchev.

Even while he was only Khrushchev's deputy, Kosygin was noted for his studied underplaying of the ideological jargon. He rarely spoke in lofty communist slogans but read his speeches as if he was genuinely familiar with technical details. At various times, he also served as finance minister, minister of light industries and chairman of the State Planning Commission.

He was also known to be an advocate of arms control negotiations. In 1962, defending the Soviet decision to back down from a confrontation with the United States during the Cuban missile crisis and calling it "a concession to sanity and peace," he said:

"Some people ask if it was necessary to yield. We think it was necessary to make a concession from both sides. This copromise is in the interest of the whole world because on that basis the danger of a thermonuclear war has been liquidated."

In 1965, he helped mediate a settlement of the Indo-Pakistani war. That same year, Kosygin was visiting Hanoi the day the United States stated bombing raids on North Vietnam.Two years later, his 1967 meeting with President Johnson at Glassboro, N.J., paved the way for the subsequent Soviet-American strategic arms limitation talks.

Twice he was personally involved in attempts to patch up the Sino-Soviet feud, one of the most pressing Soviet foreign policy problems. In 1965, he met Mao Tse-tung and in 1969 held a dramatic conference at Peking airport with Chou En-lai. Both attempts failed.

During the last few years, his foreign policy role was taken over by Brezhnev, who emerged as the top Kremlin spokesman on international issues. There were reports in Moscow recently that Kosygin's influence in the Politburo on economic issues had declined as well. If true, this was in part due to his ill health.

Occasionally, Kosygin reemerged as the Kremlin's foreign policy spokesman with his recent visits to India, Ethiopia and South Yemen. Yet it was clear that his role was due to Brezhnev's poor health at the time.

In his main role as economic overlord, however, Kosygin is likely to be judged as having failed. He had sought to revitalize the economy and help it break out of technological stagnation. He had promoted some decentralization and had experimented with using profits and sales, rather than sheer volume of output, as an indicator of economic success. On this score he was eventually rebuffed by the party, which is believed to have been afraid of political impact such reforms would have on its power.