In his first detailed assessment of the Kosovo war, NATO's supreme commander, U.S. Gen. Wesley K. Clark, said today the alliance was hamstrung by competing political and military interests that may have prolonged the conflict.

During an interview following a three-hour presentation to NATO ambassadors on the lessons to be learned from the intervention in Kosovo, Clark acknowledged that he was compelled to sacrifice basic logic of warfare to maintain the political cohesion of the alliance.

"Once the barrier to using military force is crossed, the natural desire among military commanders is to succeed by rapid intensification of warfare in order to achieve the stated objectives," Clark said.

"The lesson is we should do as much as we possibly can, as rapidly as we can do it. But to the extent that an incremental campaign was essential to maintain alliance cohesion, it was the right thing to do."

While the 78-day bombing campaign was deemed successful because it ultimately forced Yugoslav President Slobodan Milosevic to pull his troops out of Kosovo province and accept the deployment of NATO peacekeepers there, the conflict raised doubts about the alliance's capacity for crisis management, its ability to reach consensus on how to wage war and the incompatibility of U.S. and European forces.

The air war was conducted under constraints that frustrated military planners, including a desire by NATO political leaders to avoid civilian casualties and allied pilot losses as well as their refusal to consider a ground invasion until a few days before Milosevic capitulated.

While those demands complicated NATO's military mission, Clark said they were probably necessary to ensure the alliance stayed together, given the anti-war pressures felt by coalition governments in Germany and Italy.

During today's session, NATO diplomats scrutinized other weaknesses in alliance strategy, including a failure to anticipate that NATO bombing would provoke Yugoslav and Serbian forces to escalate the brutal expulsion of ethnic Albanians and thus heighten a humanitarian catastrophe that the alliance was seeking to prevent.

NATO officials said they were caught off-guard by the extent of the Belgrade government expulsion campaign, even though "Operation Horseshoe"--as the Yugoslav army called the operation--was known to have been conceived by Milosevic and his advisers last October.

"It's clear we should have put down more markers in the sand to warn Milosevic that any expansion of the violence would bring devastating damage to his own people," a senior NATO diplomat said. On the other hand, he noted that the shocking extent of that violence was a propaganda boon for NATO, securing public support for the bombing.

The NATO review showed that the alliance should have responded forcefully to the massacre by Serbian special police of 45 ethnic Albanians near the town of Racak in mid-January. But diplomats said the need to "go the extra mile" in exploring a diplomatic solution outweighed Clark's recommendation of airstrikes at that time.

The delay gave Milosevic time to bolster his forces inside Kosovo, disperse aircraft, to prepare defenses against an eventual bombing campaign and to choose the most opportune moment to launch his own offensive. As a result, the alliance lost any element of surprise.

"We realize now we were in a reactive mode nearly all the time," a European NATO ambassador said. "We were more worried about how our actions were playing to public opinion in our own capitals rather than analyzing the impact on Milosevic and his regime."

NATO leaders were clearly surprised when Milosevic did not fold after the first wave of cruise missile strikes in late March. There also was widespread disappointment that NATO aircraft were largely ineffective in the bad weather that cloaked the early phase of the campaign.

But NATO officials said the decision in April to triple the number of allied aircraft in the operation helped secure success. NATO also proved effective at moving swiftly to set up refugee camps, thus countering Milosevic's efforts to destabilize Albania and Macedonia by flooding them with expelled Kosovo Albanians. And while disavowing any tactical links with Kosovo Liberation Army guerrillas, NATO officials said key targeting information was passed through the Albanian army from KLA operatives in the field.

"We always said NATO would never serve as the KLA's air force, but they ended up serving as our surrogate army," an allied military official said.

Clark and other NATO officials say they still cannot pinpoint any single indicator of why Milosevic decided to withdraw his forces from Kosovo. "It was the last option to save his regime," Clark said. "Early on, there were many ways out of the box. But the doors closed one by one until there was no other way out."

Clark said "a multiplicity of factors" forced Milosevic to accept NATO's conditions: He failed to break the alliance's unity or shatter morale by capturing its pilots; he saw strategic airstrikes raise the hardship level for his people; he saw the likelihood of a ground invasion become serious; and he saw Russia abandon him by endorsing NATO demands to retreat from Kosovo.

The Moscow card, NATO officials say, may have been crucial because Milosevic always thought Russia would never side with its Cold War enemy. After breaking off relations with NATO at the start of the air war, Russian officials have agreed to resume contacts Tuesday at a meeting of the Permanent Joint Council that was set up in 1997 to improve Russia-NATO ties.