Top officials from NATO and the Kosovo Liberation Army were unable to agree today on the terms of a pact that would transform the ethnic Albanian rebel force into a peacetime civil defense organization, and they broke off negotiations.

The divide prompted British Lt. Gen. Mike Jackson, NATO's top military official in Kosovo, to issue a sharp rebuke to the rebel leaders and warn that they were "in danger of unsettling the future of the vast majority of [the KLA's present members] and indeed perhaps Kosovo's future as a whole." He did not elaborate.

The key issue in dispute was how many weapons can be carried by members of the new civil corps for self-defense. NATO officials insisted through a long night of negotiations that the number of armaments that can be carried at any one time be no greater than 200, for an organization with a full-time membership of 3,000.

NATO officials said they were concerned that permitting any more weapons would allow Yugoslav officials to claim that the new organization possessed military capabilities, something NATO has said it wants to prevent. Kosovo remains officially a province of Serbia, Yugoslavia's dominant republic, but all Yugoslav forces withdrew in June as NATO peacekeepers arrived after a 78-day bombing campaign by the western alliance.

According to the terms of an agreement signed three months ago, the KLA was to have ceased to exist at midnight Sunday, and by that time, NATO and the KLA were to have formally certified that the rebel group had turned in all of its weapons. But as the deadline passed, most of the rebel army's senior leadership--wearing uniforms and carrying sidearms--remained in talks with their NATO counterparts at the alliance's headquarters atop a hill overlooking this provincial capital. "You can make the rules and deadlines as needed," one NATO official said, and indeed, the demobilization deadline was extended for 48 hours.

After the talks broke off, Jackson noted pointedly that the KLA leaders would retain their posts for only another two days, until 1 a.m. Wednesday Eastern Daylight Time, under an extension approved by NATO and the chief U.N. official in Kosovo, Bernard Kouchner.

NATO already has said it accepts the KLA's assurance that its official arsenal of weaponry has been surrendered, although a spokesman affirmed today that no one knows for sure how many weapons might remain in the hands of Kosovo's ethnic Albanian and Serb citizens. "It's part of the culture in this part of the world" to have a gun, said British Lt. Col. Robin Clifford, a NATO spokesman.

The new peacetime corps being established to replace the KLA is officially charged with civilian and humanitarian tasks, such as firefighting, rescue missions and helping the citizens of Kosovo in the event of natural disasters. But KLA leaders have said openly that they regard the new corps as the centerpiece of a military defense against a future invasion by Yugoslav troops.

On Saturday, KLA political leader Hashim Thaqi told a crowd at a ceremony marking the guerrilla group's transformation that the new corps "won't be called KLA, but will be a defense force of the citizens and territory of Kosovo. I'm convinced the international community will respect the democratic right for self-declaration and referendum," he said, referring to the possibility of a plebiscite that would sever Kosovo from Serbia. "And I am convinced that you will vote for the independence of Kosovo."

An independent Kosovo is strongly opposed by Russia and the Yugoslav government. Neither the United States nor its Western allies has called openly for an independent Kosovo.

Under NATO's plan for the peacetime group, it would have no more than 3,000 active members and 2,000 reservists. But some KLA officials have opposed placing fighters in a new force with purely civilian tasks and have demanded a force with more weapons. Also in dispute is whether the unit would be described in Albanian, the language spoken by most Kosovo residents, as an "army corps"--as the KLA insists--or just a "corps," as NATO prefers.

NATO officials said the talks were not helped by recent demands from Yugoslav leaders, who have been insisting that Yugoslav troops be allowed to return to the province immediately to help protect its dwindling population of ethnic Serbs against harassment by the ethnic Albanian majority.

The agreement NATO reached with Yugoslavia in June calls for the eventual return of hundreds of Serbian troops to guard borders and monuments, but a NATO spokesman said Friday that "the time is not right yet" for this to happen.

To ward off a flare-up of violence, NATO forces in northern Kosovo have been placed on higher alert to guard against a military provocation by Serbs in the wake of the KLA's demilitarization, NATO officials said. NATO searches of homes and businesses in Serbian areas also have been stepped up in an effort to confiscate illegal weapons before they can be used. Submachine guns, automatic rifles, bayonets, grenades, mines and night vision devices have been seized in recent days.

"There are some people who are determined to destabilize Kosovo," Clifford said. NATO's Kosovo force is prepared to deal with this, he said, but he warned KLA officials that any deliberate acts of noncompliance with the demobilization agreement will be "dealt with swiftly and robustly."