MOSCOW, AUG. 6 -- Escorted by tearful family members, friends and a crowd of western journalists, pianist Vladimir Feltsman and his wife, Anna, boarded a flight for Vienna this morning with their 4-year-old son, abandoning the Soviet Union after an eight-year effort to emigrate.

Feltsman, a respected concert artist, struggled to keep his playing in touch and his career alive after authorities responded to his emigration request in 1979 by barring him from major appearances. As he left, the 35-year-old pianist could look forward to an immediate teaching post at the State University of New York and a likely career as a performer.

Yet as the Feltsmans bade farewell to a country they say they still love, their relief and elation at leaving were mixed with apprehension about their new life and bitterness toward a system that forced them to choose between East and West. "We are full of hope," said the slender, bearded pianist, who plans to move his family to New York City. "But at the same time it is very painful."

Anna Feltsman will meet a brother in New York after an eight-year separation, but she leaves behind her parents. She lingered in a weeping embrace with her mother, knowing that they may not meet again. "I consider this to be a tragedy of families," she said. "It's not right that people must leave their own countries. It's absolutely absurd that people must be divided in this way."

The Feltsmans' departure, which came after repeated interventions on their behalf by high U.S. officials, was a landmark in what has been an important shift this year in Jewish emigration from the Soviet Union. After six years in which only a small number of families were allowed to leave, an average of nearly 800 Jews a month have left since April, including several well-known intellectuals and artists.

{Upon arriving in Vienna, the pianist said, "We hope that in the States we will find our second motherland," The Associated Press reported. The Feltsmans were welcomed by Warren Zimmerman, U.S. ambassador to the 35-nation Helsinki Review Conference on European cooperation and security.}

The increased number of exit visas, although well below the record average level of 4,200 a month in 1979, has been taken as a sign of the relative liberalism of Soviet leader Mikhail Gorbachev and his desire for improved relations with the United States, Israel and other western countries.

The policy has won Gorbachev praise from both international Jewish leaders and those, like Feltsman, finally allowed to emigrate.

Still, the sudden exodus this year has also brought upheaval and pain for the large community of refuseniks, or Jews denied exit permits. In Moscow, Leningrad and other large cities, thousands of families who applied to leave during the emigration wave of the late 1970s have ended up waiting out the 1980s together, sharing their frustration and hardships after the end of detente all but closed down the way out.

The new emigration wave has meant the sudden sundering of these bonds for people given two weeks' notice to leave, and a mixture of jubilation and jealousy, hope and desperation for those left behind.

"Very frankly, it's hard to be happy," said Vera Katz, another prominent refusenik who with her husband, Simeon, and two children was granted an exit visa this week after a nine-year wait. "If I thought everyone was going to leave, I would be very happy. But knowing that we are exceptions, that we are going and so many are staying, it is hard to feel so happy. I feel pain."

Among the score of the Feltsmans' friends who made the trip to Moscow's Sheremetievo Airport to see them off this morning were several Jewish intellectuals whose longstanding emigration cases unaccountably show no sign of movement despite the recent trend. For them, farewells are becoming a part of life's bittersweet routine.

"It's slowly happened that the majority of people from my circle already emigrated. I have seen 10 families leave already this year," said Valery Soifer, a geneticist who applied to leave in 1978, one year before Feltsman. "Of course people who are waiting for a long time are suffering, and when the government permits their friends to leave, it's very hard for them."

One of the few distinct criteria perceptible in the seemingly arbitrary dispensation of visas is that of security cases. Those who, like Soifer, have been turned down on the grounds that they at one time had access to government secrets have by and large not been granted visas this year. This has been true even though many have not worked in their fields for decades and insist that they pose no plausible security threat.

Other difficulties await Jews who only now are filing applications to emigrate. While releasing many of those who have waited since the 1970s, authorities have also tightened requirements for new applicants, specifying that emigrants must have an immediate family relation -- parent, spouse, child or sibling -- living in Israel or the West to qualify. Until now, more distant relations were accepted.

The combination of increased visas and tougher rules has convinced some activists here that Gorbachev's policy is limited to removing obstacles to improved relations with the West and does not imply a fundamental change of attitude toward emigration.

"This isn't a real beginning, because they are just getting rid of the old troublemakers," said Simeon Katz, a geophysicist who plans to work at the University of Southern California after his departure. "For others, younger people, the situation has not changed."

Those suddenly singled out by the emigration authorities -- usually with a curt telephone call that arrives with no warning -- must cope with disposing of their homes and most possessions, arranging places and jobs to go to abroad, and raising $1,700 per person to pay for visa fees and plane tickets within the space of two or three weeks.

Even if material arrangements are smooth, the emigrants must face perhaps irrevocable breaks in their emotional lives. Vladimir Feltsman's father, a popular songwriter supportive of the government and reportedly opposed to his son's departure, did not appear at the airport today to see the family off.

In an interview last week, Feltsman also spoke with sadness of leaving behind the Moscow audience, which heard him as a rising star during the 1970s and packed a hall last April to hear the first and last concert he was allowed in Moscow during his emigration struggle.

"I still love this country and I love the music public, which I think is best in the world," he said. "I am 35 years old, and I want to take care of myself.

"I simply hope that I will make my wife and myself happy in the United States, and that I will realize myself as an artist," Feltsman said. "We have paid a very high price to be in the free world, and we want to believe that we won't be disappointed."

Although he views himself as a beneficiary of Gorbachev's more liberal policies, Feltsman said that real change would mean that he would not have had to leave the Soviet Union at all. "If we could freely come and go -- if I could go and make contacts in the West, make records and then return -- then nobody would ever defect," he said.

Nevertheless, the pianist is optimistic. "I believe that I will be back to perform, that things will open up here and truly change, even if it's too late for me now," he said. "I only hope it will happen before 60 years have passed, as it did for my colleague Vladimir Horowitz. Because I can't wait that long."