Russian peacekeeping troops, whom Serbs have regarded as their only sympathetic and reliable protectors in Kosovo, today shot and killed three Serbs who had attacked a group of ethnic Albanians and then fired at the Russians, Russian and NATO officials said.

The incident provoked disbelief and bitterness among Serbs near the eastern Kosovo village of Ranilug, where the shootings took place.

NATO Secretary General Javier Solana said the incident proved the Russians are living up to their duties as members of the NATO-led peacekeeping force and are not--as ethnic Albanians have charged--biased toward the province's dwindling Serbian community, whose people have a centuries-long affiliation with Russia.

"It proves that Russian troops are behaving according to their obligations," said Solana, who was visiting Pristina, the Kosovo capital.

Ethnic Albanians have greeted the Russians with hostility because Russian volunteers fought for the Serbs in their armed conflict with the Kosovo Liberation Army, an ethnic Albanian guerrilla force that sought Kosovo's independence from Serbia.

For the past two weeks, ethnic Albanians in the town of Orahovac have blockaded roads into western Kosovo to keep the Russians from moving in to protect 3,000 isolated Serbs. It was uncertain whether today's Russian action would help end the blockade. KLA officials insisted in radio broadcasts that Russians could not be trusted.

The Ranilug shootings were the latest incident in a surge of violence between ethnic Albanians and Serbs. Last week, one person was killed in Pristina when a bomb was tossed into a Serbian apartment. Over the weekend, two Serbs were wounded by gunfire near Ajnovice in eastern Kosovo, and two ethnic Albanians were wounded in an attack on a bus outside the town of Gniljane.

Also this weekend, an ethnic Albanian was killed when a rocket-propelled grenade hit his truck in a predominately Serbian district north of Kosovska Mitrovica, a city where Serbs and Albanians regularly exchange fire across a river. In western Kosovo, a Serb was wounded near Orahovac, and an unidentified man was shot and killed in his car near Djakovica.

Some NATO officials believe that the spike in attacks could foreshadow heightened violence before the KLA finishes handing over its weapons and loses its military status on Sept. 19.

Solana confirmed that it must meet that deadline despite a request from chief of staff Agim Ceku for a 10-day extention. Solana also said that the KLA's future, as part of a police or as a civilian rescue brigade, precludes its reconstitution as an army.

Kosovo officially remains a province of Serbia, Yugoslavia's dominant republic, although its ties with the Serb-led government in Belgrade are increasingly tenuous.

Today's incident began when the three Serbs ambushed a car carrying five ethnic Albanians, killing one and wounding two. The other two fled on foot.

The Serbs were beating one of the wounded ethnic Albanians when the Russians arrived from a nearby checkpoint. One Serb fired at them, hitting one soldier who was wearing a flak jacket that protected him from injury. The Russians returned the fire.

In the wake of the shooting, a group of sullen and dejected Serbs contended that there was no one left to protect them.

"The Russians sold out to the aggressors. Now they want to shoot us to prove their loyalty," said Nikola Tosic, who insisted that the ethnic Albanians in the car were armed. The initial NATO report said there was a "firefight" between the Serbs and ethnic Albanians.