Russia today ended a four-month boycott on contacts with NATO, marking an important step toward reconciliation following an angry dispute over the alliance's bombing campaign against Yugoslavia.

Ambassadors from Russia and NATO's 19 member states meeting at allied headquarters in Brussels, discussed how to improve cooperation within the Kosovo peacekeeping force. The NATO-led operation will eventually deploy more than 50,000 troops from more than two dozen countries, including 3,600 soldiers sent by Moscow.

NATO officials described the two-hour session as positive and constructive, largely because the Russians showed a willingness to start healing the breach in relations. NATO's attack on a sovereign country for the first time in its 50-year history outraged Moscow, which lambasted the allied air war as a violation of international law.

"Everyone was relieved to see a resumption in the dialogue with Moscow, because the Russian connection was the last piece of the jigsaw puzzle that needed to be put back in place," a senior NATO diplomat said.

NATO officials feared that Russia was likely to prolong the freeze because of looming parliamentary and presidential elections. With nationalists and communists expected to do well, there was concern that Russia's politicians would persist in characterizing NATO as an evil adversary, rather than a potential partner.

The Permanent Joint Council between NATO and Russia was established two years ago as a way to soothe Moscow's anxiety about the alliance's eastward expansion. It was also designed to create a security partnership that would expand cooperation in many areas, including peacekeeping, counterterrorism and halting the spread of weapons of mass destruction.

The resumption of formal contacts was supposed to take place Tuesday, but was postponed when the two sides could not agree on a common declaration of aims in Kosovo. In a brief statement after today's meeting, NATO and Russia pledged to "do their utmost to ensure equal security for all inhabitants of Kosovo, regardless of their ethnic, political or religious affiliations."

Sergei Kislyak, the Russian ambassador to NATO, warned that NATO forces must act aggressively in stripping Kosovo Liberation Army guerrillas of their weapons. He also insisted that the southern Serbian province must remain an integral part of Yugoslavia and not be allowed to evolve from an international protectorate into an independent state.

NATO officials said the next round of consultations with Russia would likely occur in September, possibly at the defense minister level. But Kislyak emphasized that any further evolution toward improved ties would depend on the West's willingness to respect Russia's security interests.