PANCEVO, YUGOSLAVIA -- Hundreds of cars were parked in ragged lines across a weedy field here on a hot Saturday morning, their hoods draped with beach towels and covered with the goods Yugoslavs are looking for: auto parts, blue jeans, hair dryers, even a stray blood pressure gauge.

This is one of the five weekend flea markets established in the republic of Serbia for private citizens, theoretically meant for the exchange of their old household goods. Similar markets exist around the shortage-plagued nations of communist-ruled Eastern Europe, serving a small but important role in satisfying consumers.

The curious thing about this place, though, was its merchants. Of more than 500 cars parked on the field one recent day, only three bore Yugoslav license plates. And although plenty of Yugoslav buyers were present, the chatter of the salesmen sounded less like Serbo-Croatian than, well, Polish. "It's true," one of them confessed. "But you're not supposed to notice that. Better say it was Chinese."

In fact, the several thousand peddlers found each week at this market, about 660 miles and three international borders from Warsaw, are almost exclusively Poles who have managed to defy Eastern Europe's elaborate restrictions on both travel and private trade.

Puttering across the continent in sedans laden with contraband, bribing border guards and abusing transit visas with a cheerful savoir-faire, Poles are once again becoming notorious this summer for subverting socialist economies with their free-lance free enterprise.

"Polish citizens are coming to our country less and less because of its beauty and monuments and more and more because of trading," complained the Belgrade newspaper Borba. "They faultlessly figure out what is lacking on one side of the border and what exists on the other, and, of course, they make a buck from it."

Trafficking in scarce goods has been a lucrative, if perilous, occupation in Eastern Europe for decades. With the collapse of their economy in the 1980s and the liberalization of their access to passports, however, Poles have made it into a mainstream national craft.

Even legitimate tourists traveling from Poland to other communist-ruled countries now routinely carry a few spare items to trade at their destination for goods scarce in Poland, customs officials say.

From there it is a short step to a real business. Polish workers frequently buy goods in an affluent socialist country such as Hungary, take them to poor socialist countries such as Romania and Bulgaria and resell them at inflated prices. They then change the local currency they receive into dollars on the black market -- often created by the traders themselves -- to carry the profit home.

Many of those stopping in Pancevo are embarked on an even more ambitious venture: a 2,400-mile round trip drive from Warsaw to Turkey. In Istanbul, the Poles -- who by now can patronize stores that cater especially to their business with Polish-speaking clerks -- buy blue jeans, designer clothes, electronics and other western goods unavailable in the East.

Then, taking advantage of the transit visas granted them through socialist countries on the route to Turkey, the Poles peddle their wares all the way home, changing the Romanian leis, Bulgarian leva, Yugoslav dinars and Hungarian forints they receive into dollars at every opportunity.

"It's the way to make the money that you can't make in Poland," was the way one trader here, a 45-year-old craftsman from Lodz, explained it. "We've driven 5,500 kilometers {about 3,500 miles} through Turkey, Greece, Bulgaria and Yugoslavia in the last three weeks and we're not through yet," he added. "But we'll go home with enough hard currency to last us until next summer."

So heavy has the flow of Polish traders along Eastern European travel routes become this summer that it has provoked special countermeasures by the Yugoslav and Hungarian governments -- and a subsequent row with authorities in Warsaw. Stung by the thousands of Poles seeking to smuggle out its salami or peddle its citizens' Turkish blue jeans, Hungarian officials this month suddenly adopted new rules singling out Poles for exceptional customs treatment.

According to the new provisions, Polish travelers passing into Hungary are required to pay a deposit in dollars based on the worth of all the potentially negotiable goods they bring into the country. When they leave, they must show they still have all those goods or forfeit the deposit. And even if the Polish travelers thus prove their innocence of contraband trading, the Hungarian inspectors are charging a 2 percent handling fee on the deposit.

The Yugoslav measures are even tougher. According to reports in the Polish state press, all travelers from Poland are simply being charged a flat fee of $30 to $100 by customs officers at the border who assume that any Polish tourist is also a smuggler. According to the Warsaw daily Zycie Warszawy, the Yugoslav inspectors no longer even bother to check Polish luggage.

Polish government spokesman Jerzy Urban said at a press conference this week that Warsaw had protested the measures of the Hungarians and Yugoslavs. "A certain number of Poles travel with the intention of trading," he said. "But this is not a one-sided phenomenon. And we think it's strange that the Hungarian authorities are singling out Poles and assigning us collective responsibility."

At Pancevo, a small town about 30 miles northeast of Belgrade, some of the Polish traders showed a hint of sly pride at their burgeoning reputation. "It just shows we're the smart ones, the good businessmen," said a young man from Krakow, who with a partner was displaying what amounted to a small hardware store atop his Polish-made Fiat. "You can find us all over Europe."

The two traders said they had been going to Yugoslavia on summer vacations for 10 years to trade and sell goods. In two months this year, they said, they expected to make between $2,000 and $3,000 -- a sum that, changed to zlotys on Poland's huge black market, would be equal to 10 years of the current average pay for a state worker.

Such astronomical gains, the product of Poland's relative poverty and the enormous value western currency has in the country, help explain why so many Poles are willing to take such risks in trading and smuggling. A tour through the Pancevo market revealed not hardened businessmen but largely common, hard-working Polish families hoping that a little initiative on their summer vacation would radically improve their living standards.

Piotr, 28, a heavy-equipment operator, and Jadwiga, 26, his wife, left their 4-year-old son in Radom, Poland, with a grandmother to make a three-week trek to Turkey and back. Their idea, they said, was to make dollars they could spend for scarce goods in Poland's hard-currency stores and change into zlotys when a pinch came.

To them, their journey was no vacation. First they invested two months' salary in a travel voucher that allowed them to get passports and Turkish visas. Then they got transit visas for Czechoslovakia, Hungary, Yugoslavia, Bulgaria and Romania and set off for Istanbul in their small Fiat, sleeping along the road and eating food they brought.

By the time they reached Pancevo, on their way back from Turkey, they had been on the road two weeks. They had designer jeans, cotton underwear and sportshirts from Istanbul to sell to the Yugoslavs -- and cartons of Kent cigarettes, the preferred bribe of officials in Romania, to ease the next leg of the trip.

"This makes a real difference to us economically," Piotr said. "And it is a kind of adventure."