Mikhail Suslov, 79, the high priest of communist dogma for more than three decades and the second most powerful member of the Soviet leadership, died yesterday after "a brief grave illness," the government news agency Tass announced today.

A medical report issued by Tass said Mr. Suslov, who suffered from "generalized arteriosclerosis," lost consciousness on Jan. 21 when blood circulation was disrupted in his brain.

Six feet tall, gaunt and near-sighted, Mr. Suslov was the eminence grise of the Kremlin and the undisputed guardian of the doctrine by which it rules. First elected to the ruling Politburo in 1952, he wielded supreme authority while remaining behind the scenes to avoid the hatred of his enemies and the envy of his rivals.

He knew no rival in the degree of his unshakable belief in communism. This, and the fact that he did not aspire to become the leader, made him not only the ultimate interpreter of Marxism-Leninism but also the kingmaker in the Politburo.

It was not that he was remarkable for any outstanding theoretical contributions or for a profound knowledge of Marxism, although he was known for possessing considerable intelligence and agility of mind. What set him apart was his ability to provide an ideological justification for practical party policies and an unusual gift for manipulating power.

He played a key role in assessing the "gains of socialism" in other countries, which made him a decisive factor in Moscow's actions ranging from the 1956 suppression of the Hungarian rebellion and ideological quarrels with Yugoslavia and China to the 1968 invasion of Czechoslovakia and Soviet attitudes toward the current Polish crisis.

In his last theoretical speech, published this month, Mr. Suslov still talked about the formation of a "new Soviet man" as being "the most important task" before the country. His last pronouncements on changes in the socialist world were addressed to Poland and included the warning that "any deviation from our revolutionary teaching brings with it fatal consequences."

His departure appears to mark the end of an era. He was the last senior survivor of the Stalin period. He joined the Communist Party in 1921, 10 years before president Leonid Brezhnev, although Brezhnev's senior by only four years. Mr. Suslov became a member of the Politburo in 1952, five years before Brezhnev was admitted to the apex of Kremlin power.

Mikhail Alexandrovich Suslov was born into a peasant family in a village on the Volga, near Ulyanovsk, on Nov. 21, 1902. As a youth he is said to have joined a committee of poor peasants protesting czarist repression.

His academic career was brilliant. He was graduated from the Plekhanov Institute of Economics in Moscow in 1928 and joined the Red Professors Institute of Economics, an institution sponsored by the party Central Committee for instruction in political science. At the same time, he taught at Moscow University and the Stalin Industrial Academy.

Among Mr. Suslov's students at the latter institution were such persons as Stalin's wife, Nadezhda Alliluyeva, and Nikita Khrushchev, who was later to replace Stalin. Both played a part in Mr. Suslov's subsequent career.

His first responsible position was that of a party watchdog. In 1931, he was made an inspector of the party's Central Control Commission seeking suspects who entertained unorthodox views. He was in charge of purges in the Ural and Chernigov regions from 1933 to 1934 and subsequently worked directly under the notorious N.I. Yezhov, the commissar of internal affairs, in one of the biggest internal bloodlettings of the Stalinist regime.

The scope of the purge, carried out from 1934 to 1937, was vast. Western experts say as many as 8 million people were placed in concentration camps. Of the 1,961 delegates to the 1934 congress of the Soviet party, 1,108 were arrested and vanished from public life. Seventy percent of the members of the Central Committee were shot.

Before Yezhov himself was shot, Mr. Suslov had been transferred to the Rostov Region as party secretary in 1937. Two years later he was named first secretary of the Stavropol Region and in 1941 he became full member of the Central Committee of the Soviet party.

He has been a member of the policy-making body ever since, and was promoted to the post of secretary of the Central Committee in 1947, a job he never relinquished.

Prior to his elevation in 1952 to the Politburo (it was known as the Presidium at the time), Mr. Suslov helped reestablish Soviet rule in Lithuania and became the main assistant to A.A. Zhdanov during the vicious ideological campaign against the "cosmopolitans" and "toadies" that carried an anti-Semitic slant.

After Zhdanov's death in 1948, the entire ideological aparat, or organization of the Central Committee, was concentrated in Mr. Suslov's hands. For a year he was the editor-in-chief of Pravda and the main proponent of the Stalinist party line.

According to Khrushchev, one day after Stalin's death in 1953, all "inexperienced" members of the Politburo, including Mr. Suslov, were expelled, although Mr. Suslov retained his other posts.

Within a year, however, Mr. Suslov was back in charge of ideology, once again regarded as an incorrigible dogmatist. The politically forceful Khrushchev was helpless in theoretical matters and he needed him to provide ideological justification for destruction of the Stalin cult. That Khrushchev turned to his old professor was not surprising. What is still a psychological and political enigma is that Mr. Suslov agreed to do it.

After that, Mr. Suslov's ascendancy in Soviet politics proceeded without interruption. He helped Khrushchev defeat the anti-party group of old Bolsheviks in 1957. Seven years later, he played a key role in removing Khrushchev himself for "adventurism" at home and abroad. It was clear that Mr. Suslov thought that Khrushchev had gone too far with his campaign against Stalin, and the subsequent partial rehabilitation of Stalin tends to confirm this.

It was said here that Mr. Suslov had declined an offer to become the party's first secretary in 1964 and had instead advanced the candidacy of Brezhnev. In doing so, he settled for the second spot in the party.

The importance of the second slot is that Mr. Suslov, in effect, exercised greater control over the Central Committee "aparat" than did Brezhnev, whose time was taken up by high-level politics and representational functions.

Little is known of Mr. Suslov's personal views or his personal life. He is related to another Politburo member, Arvid Pelshe, having been married to the sister of Pelshe's wife. Mr. Suslov's wife died in 1972 and he had led the life of an ascetic widower.

Mr. Suslov is known to have a daughter and at least one grandchild.