MATTERSBURG, AUSTRIA -- As darkness grips the forest, a group of soldiers spots an area of trampled underbrush. Using spotlights and night-vision goggles, they find tracks that vanish into a shadowy copse of beech trees.

The troops move on, hoping that their prey will be captured by a second line of men patrolling a few miles beyond.

This is the Austrian-Hungarian border, where one year after the collapse of the Iron Curtain, Austria has deployed 2,000 troops to thwart illegal immigration from Eastern Europe.

For decades, neutral Austria's modest military maintained a scant presence in the border region. Now helicopters make reconnaissance flights, reporting to scouting parties below, in the mix of marshy plain, rolling hills, forests and vineyards.

Roaming on foot, in jeeps and even on bicycles and mopeds, the soldiers fulfill a new task that has not gone undisputed.

When the government ordered the deployment on Sept. 5, Roman Catholic Bishop Johann Weber of Graz expressed shame that Austria was seeking to throw up a new Iron Curtain between itself and its newly freed communist neighbors.

"It is not a very good symbol," said Science Minister Erhard Busek, a leading critic of Austria's immigration policy. "This is not a permanent solution, and we must find other approaches."

Until the dramatic political transformation of Eastern Europe last year, Austria maintained an open-door policy that had allowed more than 2.5 million people to obtain asylum here since 1945, with most moving on to settle elsewhere.

Austrian officials vow that their country will retain its traditional role as a haven for those facing political or religious persecution, but the government is weighing new limitations on immigration by economic refugees. To encourage them to stay home, it is pressing for increased Western assistance to nearby states making the transition from controlled to market economies.

Nearly 20,000 people, more than half of them Romanians, have sought political asylum in Austria so far this year, compared with 15,790 two years ago. The Interior Ministry is seeking to deport up to 7,000 Romanians ineligible for asylum, although this plan has provoked outrage from Catholic church leaders and the International Helsinki Federation for Human Rights. State carrier Austrian Airlines has balked at a government request to carry out the deportations unless given firm assurances that the Romanians are returning home by their own consent and will not face renewed persecution.

Interior Minister Franz Loeschnak, defending the planned deportations, has expressed doubts that large numbers of Romanians can find jobs and be successfully integrated into Austrian society. In addition to those who are attempting to obtain asylum, illegal immigrants from Romania and elsewhere are swelling a clandestine labor market centered in Vienna.

Austria, bordered by Hungary, Czechoslovakia and Yugoslavia, is the gateway to the West for many East Europeans fleeing economic turmoil. With the Austrian economy outperforming other many Western European nations, immigrants often find lucrative work. But economists blame the rising number of illegal workers for the increase in unemployment to 5.2 percent of the official work force, against 4.5 percent a year ago.

Some 20,000 foreign workers on the black market took advantage of a recent amnesty allowing them to register legally, but 50,000 are estimated still underground. Austrians fear that that they will take away jobs or burden the state.

Playing to these fears, the rightist Freedom Party last month increased its representation in parliament to 17 percent, from 10 percent in 1986.

Before the army deployment, as many as 200 immigrants a day sneaked across the border. Most now trying to do so are from Romania, followed by Poles, Lebanese, Turks, Ghanaians and Iranians. There is concern that a new flood may come from the Soviet Union when visa-free travel takes effect there this fall.

Before the deployment, border residents felt threatened by the strangers whom they regarded as unwelcome intruders.

"Austria simply cannot take in all these people. Millions will come to us and Austria will overflow," said Siegfried Sereinig, a new army recruit. "Yes, it is ironic to be here at the border where there is a plaque recalling the East German refugees who came over a year ago. But now it is all too much for the local population."