Gorbachev Wins New Mandate : Soviet Union: His election as the nation’s first executive president grants him sweeping powers to pursue bolder reforms.

MOSCOW —  Mikhail S. Gorbachev was elected today as the Soviet Union’s first executive president, a powerful post with a sweeping mandate that Gorbachev wanted to pursue broader and bolder reforms.

In an overnight election, the Congress of People’s Deputies voted 1,329 to 495 for Gorbachev, who was unopposed for the post.

The 66% majority he received (out of a total that included unreturned and spoiled ballots), however, was sharply lower than the nearly 96% he got last May when he was elected president of the Congress, and it reflected the recent decline in Gorbachev’s popularity at home.

An additional 421 deputies who registered for the session boycotted the vote, presumably out of opposition to Gorbachev. The boycott meant that he received only 59% of the votes from deputies taking part in the three days of deliberations at the Kremlin.

Gorbachev, who is also general secretary of the Soviet Communist Party, had emerged as the only candidate for the post after a bruising battle Wednesday that showed how serious Soviet politics have become.

Liberal members had nearly thwarted plans for the Congress of People’s Deputies, the nation’s Parliament, to choose the president as they pushed instead for a nationwide election. Gorbachev’s critics, far more numerous than a year ago when he was elected president of the Congress, had attacked his nomination vociferously, calling him a fainthearted leader whose reforms are ruining the country.

Another parliamentary move, which failed as deputies gave final approval to a series of constitutional changes, would have withdrawn all of the amendments adopted during the special session of the two preceding days and deferred them for review at the next session.

In the end, only a dramatic characterization by Gorbachev’s supporters of the Soviet Union as a nation heading toward disaster--even civil war--rallied sufficient support to ensure Gorbachev’s election today by the Congress.

Deputies began voting late Wednesday night in 40 special booths set up in St. George’s Hall in the heart of the Kremlin, and the results were announced when the body reconvened today.

Under constitutional amendments adopted this week, the new Soviet president will have far greater powers than before, including the authority to rule by decree on many issues, to appoint and remove almost any senior civilian or military official, to veto legislation and, subject to limitations, to declare a state of emergency and suspend the legislature of any constituent republic.

With Gorbachev as the only candidate--Prime Minister Nikolai I. Ryzhkov and Interior Minister Vadim M. Bakatin withdrew their nominations--more than half of the deputies would have had to vote against Gorbachev for him to lose the post.

The position was specially designed for Gorbachev to give him the broader authority that he says is vital to embolden perestroika , as his program of political, economic and social reforms is known.

But there were moments during the long debate Wednesday when sentiments in the Kremlin’s Palace of Congresses flowed against the 59-year-old Soviet leader.

“I ask you not to vote for Gorbachev under any circumstances,” Teimuraz Avalini, a deputy from the Siberian coal-mining region of Kemerovo, told the Congress, accusing Gorbachev of bringing the country to the point of collapse.

“Gorbachev is putting his foot on the brake and the accelerator at the same time,” another deputy, Olzhas Suleimenov, a leader of liberal forces in the Central Asian republic of Kazakhstan, declared, complaining that Gorbachev is proceeding too slowly with perestroika.

Alexander Shchelkanov, a Leningrad deputy, accused the Soviet leader of “voluntarism”--of acting without due consideration of the consequences of his decisions.

Pavel Bunich, a liberal economist, expressed widely felt concern that too much power would be concentrated in Gorbachev’s hands and urged him to give up his post as general secretary of the Communist Party this summer, when the next party congress can elect a successor.

And teacher Anna Komarovskaya, like other critics, expressed her disappointment in the failure of Gorbachev’s reforms to improve living standards.

“Five years of perestroika and still there is nothing to buy,” she said.

Although Gorbachev’s election to the new post was probably never in doubt, events scarcely followed the smooth scenario that his advisers had scripted.

In one key vote--on whether the Congress should elect the new president or call a national election--Gorbachev’s supporters won the two-thirds majority required by just 41 votes.

So angry were deputies at what many saw as Gorbachev’s high-handed manner in dealing with the Congress this week that they voted only 1,542 to 368 with 76 abstentions for the president’s initial election by the Congress rather than in a national contest. With 2,250 deputies, 1,501 votes were needed for passage, with abstentions and absences counting effectively as negative votes.

“A popular vote sounds attractive, and indeed it is a great idea,” Alexander N. Yakovlev, one of Gorbachev’s closest associates in the Communist Party’s ruling Politburo, told the Congress as liberals pressed for a national presidential election. “But we must take account of the current crisis. There is a struggle now between the supporters of perestroika and those opposed to it. We are at a crucial stage.”

If Gorbachev had lost, he would have been forced to face disgruntled voters in a national election campaign this year to win the post. And that could have turned, his supporters warned, into a referendum on perestroika that might be lost from the outset.

Dmitri Likhachev, a Leningrad historian regarded as the dean of Russian culture, said that the nation is in such turmoil that a presidential election could plunge it into civil war.

“I remember the revolution of February very well, and I know where emotions can lead,” the 84-year-old Likhachev told the Congress, recalling the initial 1917 revolution that ended czarist rule but whose gains were dissipated by the weakness of its leaders until the Bolshevik Revolution the following October.

“Understand our conditions. Direct election of the president will lead to civil war. . . . Believe me, believe my experience. I am against direct elections. The election must be held here immediately. We must not delay.”

And Gorbachev’s nomination did draw warm support from other speakers.