A burgeoning real estate exchange has opened here, but it's not just location, location, location that drives the market. It's fear.

The fundamental issue is who can make a home in Kosovo. NATO forces have occupied the Serbian province with a commitment to provide safety for all nationalities, but have failed to protect the minority Serbian population from revenge attacks by ethnic Albanians.

Since the end of the NATO air campaign against Yugoslavia in June, Serbs have fled the breakaway province by the thousands. Displaced Serbs who land in Belgrade paste ads on a wall and on trees outside the main mosque, offering to trade houses in Kosovo with Albanians who live in Belgrade but who feel unwelcome and insecure.

The nearly 100,000 Serbs still in Kosovo are increasingly segregated from almost 2 million ethnic Albanians. Now, it appears that ethnic Albanians who remained in Serbia during and after the NATO bombing eventually will leave--most likely for Kosovo.

The real estate offers are deceptively simple, but the exchanges themselves are anything but easy.

"Will sell or exchange a house, a store and apartment in Pec for same in Belgrade."

"Will exchange an apartment in Gnjilane."

"Lipljan, Two houses."

Because of the lawless atmosphere in Kosovo, it is possible to make an exchange for a Serbian home that does not exist because vengeful Albanians torched it. Or the house might already be occupied by Albanians whose own houses were destroyed by Serbs.

Despite the difficulties, Serbs from Kosovo and, lately, ethnic Albanians who have long made their home in Belgrade, feel there is no other choice but to try to make a trade. "If I had money, I would buy something," said Nuhi Ibisa, a Muslim Serb from Prizren, a town in southern Kosovo. "But everything we had was put into our houses. The best I can do is try to exchange them."

Both of Ibisa's houses were burned to the ground, but she still holds title to the land where they stood. "I am bitter. At least if they had let the houses stand, it would be easier to find someone to go there. We were going to leave, so why burn the houses, too?" she asked as she scanned notices outside the mosque.

Before this year's war, about 40,000 Albanians lived in Belgrade, but that number has fallen sharply over recent months. No one seems to know exactly how many reside here now. The figure may be as low as 5,000. There is no official campaign of expulsion, but a combination of resentment over the war in Kosovo and the subsequent influx of unhappy Serbs combined to make relations precarious between Serb and Albanian. Jobs became scarce; Serbs refused to hire ethnic Albanians, many of whom were seasonal workers. "There's a general feeling of insecurity, a fear of revenge from neighbors or the regime over what happened," said Fahriu Musli, an ethnic Albanian journalist.

Musli said he has received threatening phone calls, always saying that he should leave Belgrade.

Remiz, 66, an ethnic Albanian from Macedonia, a former Yugoslav republic, owns a fruit store in Belgrade that he bought years ago from savings earned shoveling coal into heating furnaces. His windows have been smashed and the store broken into a half-dozen times in the past six months. Sometimes, passersby steal plums and grapes or overturn crates. Police, he said, do nothing to stop it. He wants to trade his store for one in Pristina, the Kosovo capital.

"I have lived here for 40 years," he said. "I never thought of leaving until now. I've never even been to Kosovo."

During the war, he sent his three children to Macedonia, where his family owns farmland. They are urging him to leave. "Making a change at this time of life is almost comical. How to start over?" he asked.

Rustem Malya, an itinerant salesman, tried to trade his house in a hillside section of Belgrade to a Serb who owned an apartment in Pristina. He had not been threatened, but his brother was beaten by neighbors, he said.

The deal quickly became a nightmare of deceit. Malya said he discovered the Serb's Pristina apartment had an unpaid mortgage, perhaps leaving him open to foreclosure. He tried to cancel the deal, but the Serb refused. Both went to court, but Malya is afraid he may not get a fair hearing. In any event, such civil suits sometimes take five years to settle.

Meanwhile, the Serb dropped off his wife at Malya's house one day, and did not come back to get her. She stayed overnight, and then another two weeks. The police would not discuss the case except to say it was up to Malya to evict her.

In Pristina, an ethnic Albanian squatter occupied the Serb's apartment, further complicating a settlement. NATO troops eventually evicted the new tenant and the Serb found another partner to trade with, but he has refused to drop his suit against Malya. There was one bright spot: the Serb's wife has moved out of Malya's house.

Malya hopes he can get a court to dismiss the suit against him. In any case, he's taking a breather from house exchanging. "This is all too much of a mess. I'll try again next year," he said.