WARSAW -- The urge to get out of the Soviet Union, despite scare headlines in Western Europe about fleeing hordes, has yet to become a panic.

Thus far, it is merely a miserable trickle that more and more Soviets seem willing to endure.

On the Soviet side of the four major border crossings into Poland, cars and buses are routinely backed up as far as five miles. The usual wait is three days.

When an impatient Pole hurrying home from the republic of Byelorussia tried to skip that queue last Sunday, an angry mob of Soviets at the Terespol crossing picked up his Polonez car and flipped it.

Polish officials say it is Soviet customs officers who are causing the delays, working with maddening deliberateness and apparently trying to discourage travelers.

At least three of the East European countries that border the Soviet Union, however, are worried that the dam could burst if economic and political conditions inside their giant eastern neighbor take a cataclysmic turn.

Poland, Czechoslovakia and Hungary are making contingency plans for a refugee disaster that their economies are in no shape to handle. Finland, too, is making preparations.

"If a horror-like scenario is played out in the Soviet Union, millions could cross our border," said Zbigniew Skoczylas, Poland's new commissioner for refugees. "These refugees could be trapped in Poland because no one in the West will take them. They could finish off our economy in three or four months."

Poland has a 600-mile border with the Soviet Union that is protected by just 360 guards. It would be impossible to physically prevent the entry of large numbers of refugees. Skoczylas said that it would take years to erect fences and other barriers, even if the government decided to do so immediately, which is not likely.

If the number of Soviets coming to Poland rises sharply, Polish authorities are planning a graduated regimen of restrictions that would start with an obligatory exchange of $20 a day. Duration of a visa would depend on how much money visitors have. There are now no restrictions.

If there is a flood of Soviets who try to skirt border crossings, there are plans to strengthen border patrols with regular army troops, some of which would be transferred east from the border with Germany.

Czechoslovakia already is opting for more guards and physical barriers. Its border with the Soviet Union is just 50 miles long, and the Prague government announced last week that it has reinforced border patrols.

Deputy Interior Minister Jan Ruml said that when the Soviet Union eases exit regulations, large numbers of refugees are expected to head for Czechoslovakia. Moscow had planned to lift travel restrictions Jan. 1, but the move has been delayed until sometime later in the year.

"If there is a huge refugee wave . . . corridors will be created at the border to channel refugees to camps where they will be given assistance," Ruml told a news conference Tuesday.

Hungary, with a 100-mile border with the Soviet Union, also has begun considering setting rules requiring visitors to exchange hard currency. If that does not work, the government may "strengthen" its border with troops and police, said Agnes Anbrus of the Hungarian Interior Ministry's refugee office.

"We don't want to close our borders. This is a period of openness," Anbrus said.

The number of declared Soviet refugees, so far, is tiny. There are only 15 in Poland (12 of whom are deserters from the Soviet army) and 50 in Hungary.

The flow of travelers and traders, however, has increased dramatically, particularly in Poland. The number of Soviets entering Poland is up 67 percent this year -- to about 4 million.

Warsaw does not yet regard these additional visitors as a problem because border records show that almost 4 million Soviet citizens also have left Poland in 1990. So far, the travelers are good for business.

Many are traders, anxious to dabble in Poland's exploding private economy. The markets around Warsaw are clogged with Russian merchants selling handicrafts and rugs, Christmas ornaments and engine parts.

Farther north in Finland, where the border with the Soviet Union is more than 660 miles long, stiff visa requirements strictly limit the number of legal visitors. The Helsinki government acknowledges, however, that its small border patrol could do little to hold back a tide of refugees.

A Finnish diplomat here said the Helsinki government does not expect significant problems. He said it has sent fact-finding teams to bordering regions inside the Soviet Union and found "a good supply of foodstuffs."

The best way to head off a possible refugee problem, according to East European officials, is for the West to assist the Soviet Union in solving its internal economic problems. "Everything has to be done to make the entire Europe and world help the Soviet Union," said Skoczylas. "If the Soviet boiling pot explodes, nothing will help."

The Polish refugee official noted that, unless there is anarchy in the Soviet Union, the most difficult hurdle that would-be refugees will have in coming to Eastern Europe is getting past their own soldiers. Radio Grodno in Byelorussia announced two weeks ago that the army had used force to prevent illegal crossings into Poland.

"From what I know," said Skoczylas, a former colonel in the Polish special forces, "the Russians will not let people leave." Special correspondent Peter Maass in Budapest contributed to this report.