ALLIES STYMIED BY MILOSEVIC'S DEFIANT STANCE.

Byline: Craig R. Whitney The New York Times

Increasingly dejected by the inability of their dazzling weapons to bring Slobodan Milosevic to heel and stop the ethnic purge of Kosovo, NATO leaders are wondering, what next?

The Yugoslav president has been impervious to a weeklong battering by cruise missiles, smart bombs, stealth planes, high-tech bombers and other state-of-the-art weaponry.

An armed invasion has been effectively ruled out, NATO officials said, and the existing strategy has only one more option left - bombing the Yugoslav president's nerve centers in the heart of Belgrade, with all the risks that carries of civilian casualties.

The alternative, NATO's top civilian official said Tuesday, would be to acknowledge that the basic premise behind the bombing strategy, that a sufficient show of air power would batter Milosevic into accepting Western prescriptions for Kosovo, was fatally flawed.

And that, in turn, would mean admitting that the world's most powerful alliance, with the world's most powerful air force at its disposal, was helpless to curb the authoritarian leader of a small Balkan country from killing and victimizing his people.

``We may not have the means to stop it, but we have shown we have the will to try,'' NATO's secretary-general, Javier Solana, said in an interview Tuesday.

For the first time, other allied officials here began talking privately about the possibility that the bombing strategy might not work. That was not the view of Gen. Wesley Clark, the top allied commander, who would not comment Tuesday on reports that he had requested but not been given permission to strike the ministries in Belgrade.

But in a telephone interview, he acknowledged that Milosevic had proved to be no pushover.

``We're up against an intelligent and capable adversary who is attempting to offset all our strategies,'' Clark said. ``There are risks and no certainties in this.''

The only certainty, the general said, was that the Serb police and military forces would continue to be ``attacked, degraded, and disrupted'' by the bombing unless Milosevic called off the attacks.

Despite the failure of this strategy so far to check Milosevic, Clark maintained a resolute stance. ``The political consensus is building, political will is building, and resolution is strengthening,'' he said of the allies.

But with that allied strategy coming under question in many European media, Russian Prime Minister Yevgeny Primakov made a lightning diplomatic mission to Belgrade on Tuesday to see whether Milosevic was ready to talk peace. He was, Primakov reported Tuesday evening to German Chancellor Gerhard Schroeder in Bonn, but with the defiant condition that the allies would first have to stop bombing. The proposal was summarily rejected.

``The core of the proposals was, Stop NATO attacks first, then we'll negotiate,'' Schroeder said after the Russian prime minister left Bonn to fly back to Moscow. ``We could not accept that.''

That left the allies where they have been for the past week, hoping that punishing attacks from the air would persuade Milosevic that he had no choice but to accept their terms.

But if that did not work, as Solana explained in the interview, there was little NATO could do except say that at least it had tried. It was too late, Solana said, for NATO to send in ground troops to fight the marauding Serbian forces even if any of the allies wanted to do such a thing.

``We have not prepared for a force on the ground,'' he said, except after a peace settlement agreed to by the Serbs. Planning for a combat operation to fight their way in, he said, would take time the allies couldn't afford if they hoped to spare further agony to the civilian population of Kosovo.

In any case, from Washington to London, Paris, Bonn and Rome, President Clinton and other allied leaders have repeatedly promised their publics that it would never happen.

The only way U.S. and European troops would be prepared to enter Kosovo, the allies all agree, is as part of an allied peacekeeping force, with the consent of both the Albanians who live in Kosovo and of the Serbs who rule over it.

Milosevic's refusal even to discuss peacekeepers dashed American efforts to mediate such a deal, including an 11th-hour mission to Belgrade by an American special envoy, Richard Holbrooke.

But a week ago, they were insisting that Milosevic withdraw his forces from Kosovo and sign the peace agreement that was worked out in France last month in negotiations at Rambouillet castle, outside Paris. The agreement, not accepted by the Serbs, provided for autonomy for the province, under Serbian rule, for a three-year transition period, and 28,000 NATO peacekeepers to enforce it.