Lines Harden in Brittle Kosovo

Three men stand watch beside the rutted track, rifles cradled in their arms, grenades clipped to their belts, in the open less than a half mile from a Serbian police base where flak-jacketed officers hunker down behind sandbags.

Alarmed by the arrival of two reporters, they level their guns. More fighters emerge from the nearby village and the foothills of the Cursed Mountains, snow-crowned crags dividing Albania and Kosovo, the ethnic Albanian-majority Serb province that has been ruled with deliberate brutality for almost 10 years.

Hard-eyed young men, they wear new camouflage jumpsuits and American combat fatigues. On their shoulders are red-and-black patches embossed with a double-headed eagle and "UCK," the Albanian-language acronym for the Kosovo Liberation Army (KLA), rebels whose fight for independence may ignite a third Balkan war since 1991.

Once limited to hit-and-run attacks, the KLA has grown bolder in recent days, openly taking over villages near the border in an apparent push to secure a corridor for moving arms and men from Albania to bases in Drenica, a region in the province's interior.

Scores of Serbs have fled their homes along the border. Clashes are reported daily between rebels and Serb police, who seem reluctant to venture out from well-defended bases and urban centers.

KLA supporters have painted out signs on the few paved roads to disorient police brought in from other parts of Serbia.

The rebels, whose strength and leadership remain unknown, reject charges by the US and its European allies that they are terrorists. They say they have no choice but to fight, citing the massacres of women and children in a brutal Serbian crackdown on the KLA in Drenica in March and April, and years of systematic civil-rights abuses and discrimination by Belgrade.

"We are not terrorists," insists a mustachioed KLA commander as he finally releases the reporters unharmed. "We are only defending our homes and families."

In stepping up its fight, the KLA is not just escalating its confrontation with Belgrade. It is also threatening to sideline Ibrahim Rugova, a moderate who has led Kosovo's 2 million ethnic Albanians in a peaceful noncooperation movement since Serbia revoked the province's autonomy in 1989 and imposed a colonial-style administration.

Should Mr. Rugova be marginalized, the United States could suffer a crushing blow to its strategy for preventing all-out war and preserving stability in the most restive corner of Europe. Its policy depends on Rugova's ability to negotiate with Belgrade an accord giving Kosovo considerable autonomy, but keeping it part of what remains of Yugoslavia, which now consists of only Serbia and Montenegro.

"The US may be playing the wrong card," warns Ardian Arifaj of Koha Ditore, an independent newspaper in Pristina, the provincial capital.

"How can it base its policy on a guy who may no longer have the political support he needs to implement a negotiated solution?" he asks.

To that end, Rugova may be hurt further by a referendum held yesterday in Serbia in which Serbs were expected to vote overwhelmingly against foreign mediation in the crisis, one of Rugova's key conditions for talks. Serbs, outnumbered 9 to 1 by ethnic Albanians in Kosovo, revere the province as the seat of their medieval empire and birthplace of their Christian Orthodox Church.

The vote is expected to trigger an agreement for new sanctions against Belgrade on April 29 by the Contact Group - the US, Italy, Britain, France, Germany, and Russia - which oversees international policy toward the former Yugoslavia. The group has been trying to pressure both sides to negotiate, but without success.

The referendum was called by Yugoslav President Slobodan Milosevic, a former communist apparatchik who rose to power in 1987 by casting himself as the savior of Kosovo's Serbs. In doing so, he unleashed the Serbian nationalist fever that led to the breakup of former Yugoslavia and the 1991-95 wars in Croatia and Bosnia-Herzegovina.

Rugova denies his leadership of Kosovo's ethnic Albanians is imperiled, pointing to his reelection in March as the unrecognized president of a self-declared "Republic of Kosova," the Albanian name for the province. He also dismisses the KLA as extremists with little support or firepower.

"They may be frustrated people, or it may be another game of the Serbian secret police to create a pretext for more massacres," says the former university professor and author in an interview. "They may be groups who could be exterminated in a couple of hours."

Says Rugova: "I am very much engaged right now in maintaining a democratic unity among the Albanian people."

But many ethnic Albanians say Rugova has suffered a massive loss of popular support to the KLA since the crackdown in Drenica, which was widely seen as proof that his noncooperation strategy has failed to wear down the Serbs' grip on Kosovo. Many also accuse Rugova of misleading them by insisting for years that the US supports their independence, which it has now made clear that it does not.

"People do not believe in Rugova and they distrust the Serbs," asserts Musa Kurhasku, a journalist in Djakovica, a town close to the border with Albania. "People are united now like never before ... for the boys [KLA] and against the Serb occupation."

The most recent evidence of discontent with Rugova came last week, when tensions over his rigid leadership style and refusal to escalate the confrontation with Belgrade exploded into an open revolt by senior members of his Democratic League of Kosova (LDK). They announced they were forming a "new" LDK.

Hidyet Hyseni, a leader of the revolt, says the new party intends to intensify the nonviolent independence struggle in order to provide an outlet for the huge frustrations that are driving ethnic Albanians to support the KLA. "I am still convinced that nonviolence has a chance," says Mr. Hyseni, a former political prisoner.

KLA fund-raisers, interviewed recently in Switzerland, slam Rugova and other moderates for seeking talks with Milosevic, who has a long history of deal-breaking. They also say Rugova's refusal to escalate the confrontation with Serbia after years of failing to make progress is tantamount to collaboration.

"The LDK says it was conducting passive resistance, but it was really doing nothing," says Bardhyl Mahmuti, a leader of the Kosovo People's Movement and former political prisoner now living in asylum in Switzerland. "The UCK was created by people ... who were sure that [Rugova's] policy would get us nowhere."

The rebels, meanwhile, say they have no interest in the maneuverings of ethnic Albanian leaders, Milosevic, or the international community.

They insist that they will win independence or die fighting for it.

"Never in my 22 years have I picked up a gun," recounts Adem, a fighter who says he left Pristina University to join the KLA after a Serbian police officer put a gun to head and ordered him to speak Serbian. "But I have no choice. I must do this for my family and myself. We have no life with the Serbs."