Five weeks after the end of a bitter ethnic war and the arrival of NATO troops in Kosovo, growing confusion among Western officials, local politicians and Kosovo's population about who controls the province is hampering efforts to begin rebuilding its tattered economy, political structures and social services.

The Western allies are preparing an ambitious multibillion-dollar program to repair war damage and bring stability to Kosovo and the surrounding region for the first time in at least a decade. But the effort has already become bogged down by major disagreements among the rival claimants to power in the Serbian province.

In the resulting power vacuum, Kosovo's myriad problems are multiplying. Thousands of vacant buildings, homes and businesses are being taken over by squatters, some of whom are investing in new, unlicensed enterprises whose legal basis is unresolved. No one is sure who owns public enterprises or who is to benefit from their revenues now that most Serbian officials have left and hundreds of thousands of ethnic Albanian refugees have returned.

With municipal offices otherwise unoccupied, former members of the rebel Kosovo Liberation Army are taking up positions as local administrators even though they lack any legal authority. Even so, the former rebels are making decisions and issuing edicts whose long-term viability is open to question.

In the meantime, fire departments have no trucks, hospitals have no ambulances or equipment, gas stations have no fuel. Electricity and water supplies function only intermittently, and telephone service is available only in parts of Pristina, the Kosovo capital, and a few other towns. Without a trained police force, "the level of lawlessness is stable on the high side," one senior Western official said.

But no one knows who to complain to -- or where.

According to NATO, the United Nations -- officially in charge of reestablishing a civilian government -- is the top authority. But almost no one here seems to heed, or even recognize, the U.N. presence. Many civilians still regard NATO and its 32,400 troops as the ultimate arbiter on civil matters. Other residents say unelected ethnic Albanian representatives, led by KLA members, are in charge.

Moreover, the KLA and the United Nations have begun to joust over matters both large and small. In one such encounter, Jay Carter, the senior U.N. official in charge of civilian government here, told a senior KLA official that all state-owned property in Kosovo is now under U.N. control. But Visar Reka, the KLA official, said he responded that "You're not the owner, you're just the manager; Albanians are the owners."

Reka and others who work in the offices of KLA political leader Hashim Thaqi, who has been named prime minister of a provisional government, say they have the authority to run the province until elections next spring. But U.N. officials refuse to recognize this claim. "To me, [Thaqi] represents the KLA, not the government; we are clear on this," said Brazilian diplomat Sergio Vieira de Mello, the interim U.N. administrator in Kosovo.

Even so, the United Nations itself is unsure how far its legal mandate extends and recently asked its lawyers to review what authority its officials are entitled to assert. In particular, the lawyers are looking at whether revenues from state-owned enterprises, such as electric and water utilities, must be placed in escrow until Kosovo's legal status is resolved or can be spent without input from authorities in Belgrade, the capital of both Yugoslavia and its dominant republic, Serbia. Kosovo's final legal status -- whether it will remain part of Serbia, for example -- is likely to take years to resolve.

For now, no one knows for sure what Yugoslavia -- and its Serbian leadership -- owns or is entitled to control in Kosovo. "Ownership is one of the toughest problems we face," said de Mello, who is being replaced this week by Bernard Kouchner of France. "If it is state-owned, it is the U.N.'s, at least during the interim administration. If it's private, we are in serious trouble."

Kosovo's ethnic Albanian majority is reasserting itself in the wake of the withdrawal of Serb-led forces and the flight of tens of thousands of Serbs from the province. More than 660,000 -- or roughly 85 percent -- of the ethnic Albanians who fled or were expelled from the province have now returned, each expecting to have considerably more say in Kosovo's governance.

Meanwhile, the government in Belgrade has complained repeatedly that provisions in the June 12 cease-fire accord offering Serbia at least a token role in policing borders and monuments in Kosovo have not been respected. It has also denounced talk of creating an independent currency for the province and has claimed rights to revenues from state-owned mines and power plants.

Much of the confusion stems from the uncertain status of the agreement signed by ethnic Albanian leaders and Western officials in France last March, which set out in dozens of pages what the new government here would look like. But Serbian officials never accepted the document, and nothing was written to replace it when the cease-fire accord was signed. Since then, the United Nations, NATO and local leaders have had to renegotiate which of its provisions will be followed.

KLA officials, for example, complain that the United Nations got off on the wrong foot by demanding that jobs at city halls, utilities and state-owned media be apportioned equally among Serbs and ethnic Albanians. The intent was to demonstrate even-handedness and to help persuade Kosovo Serbs to stay here. But the plan angered ethnic Albanians, who expected that jobs would be divided according to their proportion of the overall population -- now hovering at 95 percent.

"It means a new slavery," said Ram Buje, a KLA political official now employed in Thaqi's office, of the proposed 50-50 split. When asked about the split last Friday, de Mello indicated he was unaware of it and called it inappropriate. By Sunday, U.N. officials agreed that 330 ethnic Albanians will eventually work alongside just 60 Serbs at the city hall in Pristina, a likely model for other towns. But the city hall was closed Tuesday after the most prominent Serb there was badly beaten by an ethnic Albanian mob, which claimed he had committed atrocities during the war.

The ethnic Albanian leadership has not been the only source of friction for the U.N. mission. A U.N.-appointed consultative council was to have been established Tuesday, which would have the power to confirm the selection of mayors for each of Kosovo's 29 municipalities. It was supposed to have two representatives from longstanding ethnic Albanian political parties, one from the KLA, two independent ethnic Albanians, two Serbs, a Turk and a Muslim. The Belgrade government's local representative was not invited, de Mello said, "because the others won't come if he is there."

But some KLA officials last week created a new party that will not be represented, and the two Serbs picked by de Mello -- Serbian Orthodox Church Bishop Artemije Radosavljevic and Serbian Resistance Movement leader Momcilo Trajkovic -- announced last weekend they would boycott the commission on grounds that Serbs and Serbian interests are not being adequately protected. As a result, the council has yet to get off the ground.

De Mello acknowledged that it remains to be seen how the council will be replicated "at the district or . . . municipal level, where democratic institutions will truly be tested." Buje, the Thaqi aide, has in the meantime stepped into the vacuum by appointing mayors for 25 municipalities -- all but the four in which Serbs compose a majority of the local population.

"We are the people who know all the business," Buje said, but the government "is a mosaic. We know this is an international protectorate, but it's all mixed."

CAPTION: THE U.N.? Bernard Kouchner, the U.N. administrator in Kosovo, faces a situation in which disputes over control have bogged down reconstruction efforts.

CAPTION: NATO? Many in Kosovo still regard NATO, commanded by Gen. Wesley K. Clark, as the ultimate arbiter on civic matters, but NATO says it's the United Nations.

CAPTION: THE KLA? Kosovo Liberation Army leader Hashim Thaqi says the rebels have authority over Kosovo for now, but the United Nations refuses to recognize this claim.