Every evening, just before 6, the grandly named Chopin Express pulls out of a suburban Warsaw railway station bound for Austria. The passengers are predominantly young, enterprising and traveling out of a sense of despair.

Most are leaving their homeland for good.

The travelers aboard the daily train to Vienna form just part of the biggest wave of emigration from Poland since the communist takeover after World War II. Disenchanted with life here and future prospects, more and more Poles are turning their back on their own society with the hope of starting afresh in the West.

The birth of the independent trade union movement Solidarity in August 1980 released great hopes for reforms in the communist system. But, as the economic and political problems have mounted, the initial optimism has dwindled. Many young Poles are no longer prepared to wait to see how the revolution turns out.

Other communist countries in Eastern Europe have experienced similar waves of emigration in the past. An estimated 180,000 Hungarians fled their homeland after the Soviet invasion in 1956. And in 1968, the crushing of Czechoslovakia's experiment in "socialism with a human face" resulted in an exodus of 100,000 Czechoslovaks. What is remarkable about the present exodus from Poland, however, is that it is taking place before rather than after any major act of repression by either the Polish authorities or the Kremlin.

This year, according to officials here, the number of permanent Polish refugees is likely to reach the 1968 Czechoslovak level. Another 100,000 or so Poles are believed to have extended their stay in the West on a temporary basis. In the event of a Soviet invasion or the imposition of martial law, they too are unlikely to return.

By contrast, in 1980 only 8,000 or so Poles stayed permanently abroad.

The refugees leave by whatever means they can. Practically every Polish tour group to the West loses one or two of its members these days, and sometimes the number of defections is spectacular. When the Polish cruise ship Stefan Batory docked in Montreal last month, 106 passengers and four crew members asked for asylum.

The rate of attempted or successful hijackings of Polish internal flights by would-be emigrants is running at two or three a month. Last September, for example, a group of 12 young men hijacked a Warsaw-bound plane to West Berlin. Another 12 passengers took the opportunity of staying in the West with the result that, when the plane finally got back to Warsaw, it was half empty.

The most popular route to the West, however, is the Chopin Express.

The scene at Warsaw's Gdansk railway station the other day, as the train was preparing to leave, was somber and sad. Practically all refugees travel under the guise of tourists and are thus violating Poland's passport laws, which require them to return home by a fixed date. Final goodbyes with family and friends had been said long before and the platform was almost empty.

Asked why so many people were traveling to Austria, a railway guard said: "That is the private secret of each person aboard. None of them will discuss their real motives with a stranger. It's only once they get to Vienna that they declare themselves refugees."

He looked around at the dreary, ill-lit station and added: "I can't say I really blame them."

Emigration remains a sensitive topic in Poland, and is strongly discouraged by the government. There is, therefore, little documentation on the reasons for the recent upsurge. But the evidence suggests that it is due to a mixture of liberalized passport regulations and a growing feeling of hopelessness about conditions in Poland.

Maciek, a 30-year-old interior decorator who is planning to emigrate to Australia, said he was fed up with the empty shops, Poland's maddeningly inefficient economic system and what he described as "all the communist jargon and double talk" on radio and television.

"I have never been abroad before. But there's a little tic in my brain that keeps on telling me that life is better in the West," he said in an interview given on the condition that he would not be quoted by his full name.

Maciek said he had been planning to leave Poland for a long time. Ten years ago, he explained, he had been denied a passport to go to West Germany because the police objected to his long hair and "unruly behavior" as a student. It was only this year that he thought it worthwhile reapplying, and the passport was duly issued.

Asked whether he supported Solidarity, he replied: "Sure, I'm all for them. But I don't think they've much chance of changing this system in a positive way."

Anna, a 28-year-old Solidarity activist who is hoping to go to America, said her main reason for leaving was that she could not lead a normal life in Poland.

"I would have to wait another seven or eight years to get an apartment of my own. I feel nervous here, as though I'm always having to fight against something," she complained.

If Maciek and Anna do finally succeed in leaving Poland, they will be following a well-trodden path. Emigration has been a recurring feature of Polish history, particularly at times of crisis. In the 19th century, a succession of insurrections against Russian rule produced wave after wave of political exiles. The most dramatic took place exactly 150 years ago, following the collapse of the 1830 uprising, when virtually the entire Polish intelligentsia moved to Paris.

Among the Polish exiles living in France at that time was Frederic Chopin, the composer who has given his name to today's Vienna-bound train.

The tradition of emigration, for both political and economic reasons, continued into the 20th century when Poland again became an independent nation. Edmund Osmanczyk, a journalist who chairs the subcommittee on citizenship in the Polish parliament, estimates that today every second Polish citizen has a close relative living abroad.

In an interview, Osmanczyk insisted that the present wave of emigration was unique because it was exclusively economic in character.

"We have reached a stage in our history, for the first time in over 200 years, when not a single Pole can say he is forced to ask for asylum abroad because of persecution for his political beliefs," he said.

The issue of motivation for emigration is controversial since some recipient countries, notably the United States, give priority to applicants for political asylum. This practice has been much criticized in Poland. Some would-be emigrants say that to gain admission to the United States they are obliged to invent instances of political repression.

Osmanczyk is leading a campaign in parliament for major changes in the citizenship law that would allow Poles to come and go as they please and effectively put an end to the siege mentality characteristic of a communist state. He also hopes to help an estimated 1 million Poles now traveling abroad as stateless citizens since the Polish authorities refuse to renew their passports.

The slogan Osmanczyk has chosen for his campaign is "a passport in every pocket" by which he means that every Pole should have the right to a five-year passport valid for all countries in the world.

Under present regulations, Poles have to return their passports to the police after each trip abroad. Anyone who stays longer than he should in the West can be deprived of the right to travel for up to five years.

But the rules have been relaxed significantly over the past year. The authorities no longer insist on keeping at least one member of the family home as "hostage," a practice that used to be a major obstacle to emigration. The number of passports issued has risen from around 600,000 in 1980 to about a million this year, many more than any other Soviet Bloc country.

The mass exodus from Poland has caused considerable problems for Western countries, particularly Austria, which has had to find food and accommodations for about 23,000 Polish exiles. Most end up at the Traiskirchen refugee camp near Vienna, where they are interviewed by Western immigration officials.

Poles who have been to the camp paint a grim picture of conditions there. The immigration procedure usually takes well over six months. In the meantime, the refugees have to put up with overcrowded dormitories, poor food and a constant stench. Fights often break out between different groups .

This first taste of life in the West is enough to deter some refugees. Every day, several dozen would-be Polish emigrants drift back to Warsaw aboard the Chopin Express, their hopes shattered once again.