A Communist Party official held forth briefly on the sins of alcohol one recent Saturday evening here, addressing a drunk he and a local policeman had cornered.

Within seconds, the audience mushroomed, as strollers in the damp pedestrian underpass near the Kremlin clustered round, and hung closely on the official's words. The crowd watched as the drunk was led away a few minutes later, then dispersed into the Moscow night.

The antialcohol campaign had just begun, and the ad hoc crowd's anxious reaction to it -- one of new Soviet leader Mikhail Gorbachev's first and strongest initiatives to affect the public directly -- is symptomatic of the rising sense of expectation sweeping the Soviet capital and, apparently, other parts of the country.

To a visitor returning to the Soviet Union for the first time in six years, this atmosphere of renewed hope is startling. While Moscow's buildings seem the same, subtle changes in the spirit of the city are noticeable.

In 1979, a spiritual and economic slump had set in. Leonid Brezhnev was ill, the steady economic growth of his early years had begun to taper off, consumer goods were short and the spirit of detente had begun to fade.

Most important, the prospects for real change were dim. Brezhnev and all his advisers were aging. The wheels that move Soviet life were turning in place. Conversations among friends turned, inevitably, to the shortage of good meat and to the bad weather.

As the 54-year-old Gorbachev moves to invigorate Soviet life, his gusto and gall have appealed to Russians, lifting them into a mood of cautious optimism. Even though Gorbachev has made few concrete changes, Soviets seem keenly aware that he has set high goals and on edge about whether he will succeed. So far, his fighting approach to deep-seated social ills like alcoholism and public corruption have impressed them. "We all know that alcoholism is a big problem," said a young engineer in Moscow, "and it's high time someone did something about it."

Gorbachev's relative youth, too, has given Russians confidence in his chances for success. In a country where "young man" is a common form of address, even to those over 40, Soviets seem delighted that they now have the youngest party general secretary since Josef Stalin, at 43, first took the job in 1922.

One 25-year-old Leningrad dock worker explained Gorbachev's early public appeal: "The main thing is that he is young. That has given us some reason for hope and something to look forward to."

In the public eye, Gorbachev's vigor, heartiness and accessibility enhance the general sense that he is bringing on something new. In contrast to past leaders, who at best might have waved briefly to public gatherings in ceremonies at the Kremlin, Gorbachev has approached crowds directly, in a Moscow factory in April and in a well-publicized appearance on the streets of Leningrad last month. The effect is a rare feeling in the Soviet Union that the leader is close to the people and personally concerned about improving everyday life.

The images of Gorbachev presented to the Soviet public accent those positive feelings. Television shots of the Soviet leader working crowds in Leningrad last month contrasted sharply with pictures of a wheezing Konstantin Chernenko shown shortly before he died last March.

In the period which Gorbachev now hopes to supersede, public morale had seemed to decline. The rate of growth in output clearly did so. Given the limited selection of goods to buy, the Soviet public hoarded money at an annual rate of 11 percent, by western estimates.

Russians' expectations apparently dulled, too. Relations with the West worsened, and so the opportunities for contact between Soviets and westerners diminished.

Now, the Kremlin is encouraging Soviets to look to the future. Slogans all over Moscow urge citizens to get ready for the 12th Communist Party congress, which is more than seven months away. A five-year plan, and major personnel changes in the powerful Central Committee are expected to emerge from the congress.

Gorbachev, orienting Soviets toward the future, called in a much-discussed speech in Leningrad last month for 4 percent annual economic growth -- a 25 percent increase over 1984 levels.

In Moscow, consumer goods still seem scarce. But some small pleasures accent the positive expectations. Last week, vendors on busy Gorki Street were selling bags of frozen strawberries and pineapple. Dabs of black caviar on bread were offered at 60 cents each. Lines formed quickly, and the rare treats went fast.

Still, in this city where change is slow, the bureaucracy stifling and people wear their customs like winter coats, renewed expectations are cautious and expressed subtly, if at all. One retired teacher asked her visitor many enthusiastic questions about the changes in the air, but became elusive when she was questioned in turn.

Muscovites tend to be guarded in their optimism because they have heard calls for changes before and seen few of them materialize. In his later years, Brezhnev publicly recognized the need to improve the economy. But Brezhnev was not strongly committed to economic reform, and neither of the next two Soviet leaders lived long to enact much change.

Brezhnev died in October 1982. His successor, Yuri Andropov, died 14 months later and was followed by Chernenko, who died 13 months after that. The Soviet public had only brief glimpses of their aging leaders, and the prospects that everyday life and the standards of living would improve apparently were judged to be dark.

Gorbachev's chances are viewed differently because he is expected to have more time to see his plans through. Perhaps to keep anticipation from bounding too high, Gorbachev, in his Leningrad speech, stressed that sacrifice and all-out efforts from the populace must be sustained over time, that change will not come in a year or two.