PARIS — Every time Radovan Karadzic, the onetime Bosnian Serb leader, appears in court on war crimes charges, he has hammered on one recurring claim: a senior American official pledged that he would never be standing there.

The official, Richard C. Holbrooke, now a special envoy on Afghanistan and Pakistan for the Obama administration, has repeatedly denied promising Mr. Karadzic immunity from prosecution in exchange for abandoning power after the Bosnian war.

But the rumor persists, and different versions have recently emerged that line up with Mr. Karadzic’s assertion, including a new historical study of the Yugoslav wars published by Purdue University in Indiana.

Charles W. Ingrao, the study’s co-editor, said that three senior State Department officials, one of them retired, and several other people with knowledge of Mr. Holbrooke’s activities told him that Mr. Holbrooke assured Mr. Karadzic in July 1996 that he would not be pursued by the international war crimes tribunal in The Hague if he left politics.

Mr. Karadzic had already been charged by the tribunal with genocide and other crimes against civilians.

Two of the sources cited anonymously in the new study, a former senior State Department official who spent almost a decade in the Balkans and another American who was involved with international peacekeeping there in the 1990s, provided additional details in interviews with The New York Times, speaking on condition that they not be further identified.

The former State Department official said he was told of the offer by people who were close to Mr. Holbrooke’s team at the time. The other source said that Mr. Holbrooke personally and emphatically told him about the deal on two occasions.

While the two men agreed, as one of them put it, that “Holbrooke did the right thing and got the job done,” the recurring story of the deal has dogged Mr. Holbrooke.

Last summer, after more than a decade on the run, Mr. Karadzic was found living disguised in Belgrade, Serbia’s capital. He was arrested and sent to the International Criminal Tribunal for the former Yugoslavia in The Hague for his trial, which is expected to start this year.

Asked for comment for this article, Mr. Holbrooke repeated his denial in a written statement. “No one in the U.S. government ever promised anything, nor made a deal of any sort with Karadzic,” he said, noting that Mr. Karadzic stepped down in the summer of 1996 under intense American pressure.

“In subsequent meetings, as a private citizen, I repeatedly urged officials in both the Clinton and Bush administrations to capture Karadzic,” Mr. Holbrooke said. “I am glad he has finally been brought to justice, even though he uses his public platform to disseminate these fabrications.”

Mr. Holbrooke declined to accept further questions and did not address the specifics of the new accounts.

Mr. Karadzic, by insisting that he is exempt from legal proceedings, has now forced the war crimes tribunal to deal with his allegations, illustrating the difficulty of both administering international justice and conducting diplomacy.

In December, tribunal judges ruled that even if a deal had been made, it would have no bearing on a trial. They said no immunity agreement would be valid before an international tribunal in a case of genocide, war crimes or crimes against humanity. Mr. Karadzic is charged with all three.

But Mr. Karadzic has appealed and filed motions demanding that prosecutors disclose every scrap of confidential evidence about negotiations with Mr. Holbrooke. He has asked his lawyers to seek meetings with American diplomats.

His demands have led the court to write to the United States government for clarification.

Peter Robinson, a lawyer for Mr. Karadzic, said that he had received a promise from Washington that he could interview Philip S. Goldberg, who was on the Holbrooke team meeting in Belgrade the night the resignation was negotiated.

“Goldberg took the notes at that meeting,” Mr. Robinson said. “The U.S. government has agreed to search for the notes and provide them if they find them.”

A State Department spokesman said that the government was cooperating with the tribunal, but would provide no further details.

Mr. Holbrooke, who brokered the peace agreement that ended the Bosnian war in 1995, returned to Belgrade in 1996 to press Mr. Karadzic to resign as president of the Bosnian Serb republic. Mr. Holbrooke’s memoirs recount a night of fierce negotiation on July 18, 1996, but make no mention of any pledge of immunity.

The Purdue University study, “Confronting the Yugoslav Controversies: A Scholars’ Initiative,” says that Mr. Holbrooke “instructed his principal assistant, Christopher Hill, to draft the memorandum to be signed by Karadzic,” committing him to give up power.

Mr. Ingrao said Mr. Holbrooke used Slobodan Milosevic, then the Serbian leader, and other Serbian officials as intermediaries to convey the promise of immunity and to reach the deal with Mr. Karadzic.

“The agreement almost came to grief when Holbrooke vigorously refused Karadzic’s demand, and Hill’s appeal, that he affix his signature to it,” the study says, citing unidentified State Department sources.

The study, the product of eight years of research by historians, jurists and social scientists from all sides of the conflict, was an effort to reconcile disparate views of the wars that tore the former Yugoslavia apart in the 1990s, Mr. Ingrao said.

Neither Mr. Hill nor Mr. Goldberg responded to requests for interviews for this article.

In an interview, the former State Department official, who had access to confidential reports and to members of the Holbrooke team, said that during that evening in 1996, Mr. Milosevic and other Serbian officials were on the phone with Mr. Karadzic, who was in Pale, Bosnia.

The former official said that Mr. Karadzic wanted written assurances that he would not be pursued for war crimes and refused to sign without them.

“Holbrooke told the Serbs, ‘You can give him my word he won’t be pursued,’ but Holbrooke refused to sign anything,” the official said. Mr. Holbrooke could make that promise because he knew that American and other Western militaries in Bosnia were not then making arrests, the official said.

There were some 60,000 American and NATO troops in Bosnia, but the soldiers had no orders to arrest indicted Bosnians, for fear of inciting local rebellion.

In the brief statement Mr. Karadzic eventually signed, he agreed to withdraw “from all political activities” and to step down from office. It carried the signatures of Mr. Milosevic and four other Serbian leaders acting as witnesses and guarantors. It did not include any Americans’ names and made no mention of immunity.

The American who was involved in peacekeeping insisted in an interview that Mr. Holbrooke himself told him that he had made a deal with Mr. Karadzic to get him to leave politics. He recalled meeting Mr. Holbrooke in Sarajevo, Bosnia, on the eve of Bosnian elections in November 2000, just after Mr. Milosevic had finally been ousted from power in Serbia.

Mr. Holbrooke was worried about the outcome of the Bosnian vote because he knew that Mr. Karadzic was still secretly running his nationalist political party and picking candidates, including mayors and police chiefs who had run prison camps and organized massacres.

“Holbrooke was angry; he was ranting,” the American recalled. He quoted Mr. Holbrooke as saying: “That son of a bitch Karadzic. I made a deal with him that if he’d pull out of politics, we wouldn’t go after him. He’s broken that deal and now we’re going to get him.”

Mr. Karadzic’s party won those elections in the Bosnian Serb republic. Shortly afterward, he disappeared from public view.

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