Party Leader in Moscow Is Replaced : Soviet Union: With social discontent growing, he was an election target.

Lev N. Zaikov, the tough Communist Party apparatchik who has served as party leader in Moscow for the last two years, was replaced Tuesday in an apparent effort to give the party a more human face before local elections early next year.

Zaikov, 66, was appointed as President Mikhail S. Gorbachev’s deputy on the Soviet Defense Council, and well-informed sources said he was given the task of overseeing further military cutbacks and pushing the conversion of the munitions industry to civilian production.

But the immediate effect, according to the official news agency Tass, was to replace Zaikov with his more dynamic and popular deputy, Yuri A. Prokofiev, 50, an economist and longtime party official in the Soviet capital, who was elected on a secret ballot as one of three candidates for the post.

With social discontent growing in Moscow and elsewhere, Zaikov, as a member of the party’s ruling Politburo, already had become an election target for opposition groups, which saw a chance to embarrass the leadership further by defeating him in the early spring elections.

“He is unelectable,” a senior Soviet journalist said of Zaikov. “He has no sense of humor--absolutely zero--and people, the ordinary people, our narod, absolutely pain him. But his defeat would be a defeat for the party, a defeat of a member of the Politburo in the capital, and that would have irreparably damaged the party’s prestige. The choice was go now or go later--but better now.”

If he lost the election, Zaikov, under rules laid down by Gorbachev, would have to be retired from the Politburo, as the Leningrad party chief was after losing his bid last March for election to the Congress of People’s Deputies, the national assembly.

In his new post, Zaikov apparently will take over supervision of the whole Soviet military-industrial complex at a crucial time. The country is in the midst of cutting back its armed forces, scaling down its defense industries and radically shifting its strategic orientation.

Gorbachev, who participated in the Moscow party meeting, said the leadership wanted Zaikov to focus on his work as a secretary of the party’s Central Committee and on the Defense Council in view of the importance of the tasks there, according to the official news agency Tass.

Although the abruptness of the move suggested that Zaikov had been dismissed from the Moscow post, his national standing may not have been seriously diminished. At least for now, he retained his positions as a Politburo member and as Central Committee secretary--and he received the thanks of the Moscow committee for his time there.

Zaikov, who began as an apprentice mechanic in Leningrad while it was under German siege in World War II, had spent most of his career in the Soviet defense industry, working for 15 years as the director general of an armaments plant in Leningrad.

In 1976, he was chosen to be mayor of Leningrad, then the party leader there and, in 1985, he was brought to Moscow as the senior party official in charge of the defense industry. When Boris N. Yeltsin, the flamboyant populist, was replaced two years ago as first secretary of the Moscow party, one of the most important political jobs in the country, Zaikov was appointed to succeed him.

Gray and dour, Zaikov has in recent months stressed the need for ideological orthodoxy even as the country moves through political and economic reforms. Many Soviet political analysts saw an alliance on such issues with Yegor K. Ligachev, the leading conservative within the Politburo.

Zaikov has sought to promote scientific and technological progress but has repeatedly called for limits on the process of political reform, particularly glasnost, or greater openness.

In the parliamentary elections last spring, Yeltsin defeated the whole party apparatus in the first multiple-candidate elections here since the earliest days of the Soviet state more than 70 years ago. Yeltsin won 89% of the vote to win Moscow’s at-large seat despite efforts of the party machine to elect the director of an auto plant to represent Moscow.