On one side of a major traffic circle in this provincial capital this evening stood a Yugoslav armored personnel carrier surrounded by laughing and joking Serbian civilians. On the opposite side, more than a dozen British light tanks and trucks were surrounded by curious ethnic Albanian youths.

No one appeared uneasy, and for a few minutes it seemed impossible that Yugoslavia and Britain could have been on opposite sides of the 2 1/2-month war that ended last week. As darkness fell, however, shots rang out from some of the tall buildings in the city center, and the 1,700 British soldiers in Pristina hunkered down for an uneasy night.

On Day 2 of the deployment of NATO forces inside Kosovo, the separatist province was filled with a surreal mix of tension and peace as government security forces prepared to withdraw and NATO peacekeepers arrived in increasing numbers. Yugoslav troops casually carried their guns past NATO tanks; NATO police directed traffic a few miles from Yugoslav army checkpoints; Serbian civilians gestured angrily at arriving NATO troops; NATO tanks trained their cannons on Yugoslav gun emplacements.

In the annals of war, the presence of two bitter and heavily armed foes on the same territory at the same time is almost unknown. But here in Kosovo, it seems to be working reasonably well. Violence has flared in a few spots: German NATO troops came under fire in the tense western city of Prizren and killed one Serb. British paratroops here shot a Serbian police reservist to death. But in large measure, victor and vanquished have not run afoul of each other -- although the mood seesaws between cooperation and confrontation.

On Saturday afternoon, for example, the first few hundred NATO troops had made it to the center of Pristina. But they were withdrawn after dusk when top NATO commanders decided, as one soldier put it, "It was just too soon to be there . . . that we needed more time to let things settle." Scattered gunfire erupted throughout the night.

This afternoon, several British Challenger tanks at a base established in Pristina's bus station by the King's Royal Hussars Battle Group had trained their 120mm cannons on a Yugoslav light tank stationed on a ridge to the west of the city. The tank, in turn, had trained its cannon on them. "We are just itching to let them have it," said one British officer with the group.

Capt. John E. Carey-Hughes, a commander of the unit, said he was struck by how many vastly different encounters his men have had with people in Kosovo. "On the one hand, you've got children handing me flowers; on the other, you've got [Yugoslav army troops] coming to the bus station, waiting for a chance to go north with their guns in their hands. It's surreal."

When 1,700 NATO troops arrived at the southern edge of Pristina today, they had to compete for space on a major highway with dozens of red tractors driven by Serbs who said they were fleeing the Kosovo cities of Suva Reka and Prizren for fear of reprisals from ethnic Albanians. "There is no police and army around anymore. There are terrorists around," said one Serb named Marko, who declined to give his last name.

Another fleeing Serb, Stanislav Miskovic, said he had concluded that NATO troops would not be dispersed rapidly enough to protect his family in the village of Ljubisht. "Before NATO arrives, our heads will go," he said.

According to NATO's estimate, roughly 10,000 Yugoslav troops have left Kosovo, a province of Serbia, the dominant republic of Yugoslavia. The remaining 30,000 are supposed to withdraw in phases by next Sunday, although many NATO officials say the pullout is going more slowly than it should and express skepticism that the deadlines will be met.

At least a fifth of the planned NATO force of about 50,000 peacekeepers had entered Kosovo by midday today, and their presence became obvious not only in the capital but in scores of towns in the southern region of the province.

In Kosovo's Drenica region, west of Pristina, most Serbian Interior Ministry police have already departed, while Yugoslav army troops are just beginning to pack up. Several who declined to give their names said they were happy to go after more than a month of military duty in Kosovo during NATO airstrikes. "The politicians [in Belgrade] did this," said one soldier. "It happened in Croatia and Bosnia, and even back then it was the politicians' fault."

Many Yugoslav troops in Drenica waved amicably at passing vehicles from lawn chairs situated beneath overhanging trees or in front of burned-out buildings. But heavily armed members of the White Eagles militia unit associated with radical Serbian nationalist Vojislav Seselj instructed several reporters to go to the nearest police station and warned that they could be shot at any time by "terrorists."

A bedroll and a mattress sat in the middle of the road north of Glogovac, evidently left during a hasty departure. A half-dozen nearby sniper nests were vacant. Plumes of smoke rose from several homes in the area, and a red sedan was ablaze outside a building south of the city that was occupied by a handful of Interior Ministry police. As its windshield melted from the heat, they tidied up a garage that had recently been a sandbagged bunker.

"Nothing is very defined" about the withdrawal, said a soldier named Miroslav, who was turning cars away from the entrance to the Pristina airport on instructions -- he said -- of the Russian airborne troops who deployed there today. "We have 11 days to get out," he reasoned. "When we get our orders, we'll withdraw, and I'll go to Serbia" proper.