As the NATO bombing campaign against Yugoslavia got under way in March and talk of war crimes indictments against Yugoslav President Slobodan Milosevic and other Serbian leaders intensified, a loose network of antiwar law professors in Canada, Norway, Greece, Britain and France began plotting another strategy.

Communicating by phone and e-mail, the professors began building a case for war crimes indictments against NATO. By the end of the 78-day air offensive, they believed they had "overwhelming evidence" to demand the criminal prosecution of the leaders of the United States, Britain and other alliance countries, as well as NATO's senior military commanders.

Most legal scholars say the professors have a pretty weak case, noting that accidental civilian deaths caused by NATO bombs fail to meet the commonly accepted standard for war crimes. Even so, the legal campaign against the Western alliance has taken on a life of its own.

In an effort to demonstrate independence and even-handedness when the Kosovo war ended last June, prosecutors at the U.N. International Criminal Tribunal for the Former Yugoslavia began an internal review of the charges brought by the professors and others. Seven months later, the tribunal's chief prosecutor, Carla Del Ponte, is poised to decide whether to launch a formal investigation or to drop the matter entirely, as seems most probable.

The merits of the anti-NATO charges aside, the tribunal's reliance on the military assets of the Western powers to track down war crimes suspects makes it unlikely that any prosecutor would turn against a main source of intelligence and arrests. But the mere consideration of the charges by the tribunal already has irritated the United States and other NATO governments. Even the tribunal's most ardent champions in the human rights community and elsewhere are worried that the case may have damaged its reputation through an exercise in dangerous relativism.

Del Ponte ventured into the belly of the beast today with her first visit to NATO headquarters in Brussels for a meeting with the alliance's decision-making North Atlantic Council. According to Graham Blewitt, the tribunal's deputy prosecutor, almost all of the discussion was about NATO cooperation in arresting indicted war crimes suspects--especially one from an earlier Balkan war, former Bosnian Serb political leader Radovan Karadzic.

The accusations leveled at NATO leaders were raised by two people at the table, he said, and Del Ponte responded by repeating the tribunal's position that it has a statutory responsibility to investigate all alleged war crimes in the recent Balkan conflicts.

Del Ponte and her staff prepared for more of a confrontation than they got. "We were concerned about the potential harm this might do to our relations with NATO," Blewitt said. "But we were told that NATO is not above the law and that for the tribunal to ignore the charges would have affected the integrity of the tribunal. And that is our position, too."

Those charges are sweeping. Michael Mandel, a Canadian law professor who has led the effort against NATO, describes the bombing campaign as "a coward's war . . . not even partially legitimized by the Security Council of the United Nations."

What the NATO leadership portrayed as the first humanitarian intervention by great powers--to curtail the killings and mass deportations of ethnic Albanian civilians in Kosovo--Mandel called "a terrorist war against the people of Yugoslavia to force President Milosevic to give up." What has been reported widely as a military targeting process slowed and hampered by disagreement among allied leaders--and one vetted with unprecedented caution by lawyers obsessed with avoiding civilian casualties--Mandel described as "all-out, total war."

NATO bombing from high altitudes "placed all the risk on civilians and made the military immune from risk; this is a violation of the Geneva conventions," he said. The post-World War II Geneva conventions laid out the modern rules of war that are the legal foundations of the tribunal's jurisprudence. In a telephone interview from Toronto, where he teaches at York University's Osgoode Hall Law School, Mandel said "most of the world" agrees with his position. As for Milosevic's indictment by the tribunal in May, two weeks before the end of the bombing, Mandel said it was issued "with indecent haste" and was "dictated by the P.R. needs of NATO" to demonize its chief adversary.

Mandel and his colleagues prepared their complaint and met in June with Del Ponte's predecessor, Louise Arbour, and her staff in The Hague. Arbour ordered a preliminary review of the evidence and the applicable law. She was replaced in September by Del Ponte, who received the staff report just before Christmas. A tribunal source said it contained no recommendations and did not even merit the term "investigation"; the source said "it was an internal memorandum."

Views differ about Del Ponte's attitude toward the NATO dossier at a time when she has more pressing objectives. Before today's meeting, NATO officials indicated they had been assured by Del Ponte that she would not carry this exercise far and that she suggested she was embarrassed by having to deal with a tendentious process inherited from her predecessor.

"Nobody seriously thinks Del Ponte will even try to make a case against Clark or Solana," a senior NATO said, referring to U.S. Army Gen. Wesley Clark, NATO's top military officer, and Javier Solana, the Spanish diplomat who was NATO secretary general during the Kosovo conflict. "It's a ridiculous situation, and it's made a lot of people angry, including Del Ponte."

But one former and one current U.S. official familiar with the U.N. tribunal's work said Del Ponte had given the complaint needless exposure and credibility--and painted the prosecutor's office more squarely into a corner--by discussing the existence of the internal report in the news media and stressing her prerogative to investigate.

Paul Williams, a war crimes expert at American University in Washington, objected vehemently to the implied parity of offenses by the two sides in the Kosovo conflict--that is, accidental casualties caused by NATO and widespread killings and mass expulsions carried out by Serbian and Yugoslav forces.

By publicly launching an internal review of the matter, even one bound for nowhere, Williams said, the tribunal was tacitly accepting the comparison--and revealing itself to be politically driven. "You become credible by doing independent prosecutions, not by doing pseudo-prosecutions," he said in a telephone interview from Washington.

On the merits, Williams and other experts said, Mandel and his associates don't have a persuasive case. "The law is set up to prevent intentional targeting of civilians or civilian property, or grossly negligent targeting," he said. "But NATO appears to have used extreme diligence in avoiding civilian casualties."

Williams and others in the international justice community also fear the NATO war crimes case could make the alliance less cooperative in arresting war crimes suspects and stiffen U.S. reluctance to sign a 1998 treaty on establishment of a permanent international criminal court.

Correspondent William Drozdiak in Berlin contributed to this report.

CAPTION: Yugoslav troops work to clear the rubble of a Belgrade hospital wing after a NATO missile landed near the facility last May, at the height of Kosovo conflict. Yugoslav officials said at least three people died in the blast.

CAPTION: JAVIER SOLANAThe secretary general of NATO during the 2 1/2-month air bombardment of Kosovo is among alliance leaders accused of war crimes by the antiwar professors.

CAPTION: CARLA DEL PONTEThe chief prosecutor for the war crimes tribunal in The Hague says her office has a responsibility to investigate the allegations against NATO.