When a senior Iraqi delegation arrived in New York on May 1 to finish plans for the resumption of U.N. inspections in Iraq, a key member of the team was missing. Jaffar Dhia Jaffar, widely regarded as the father of Iraq's secret nuclear weapons program, had been held up by American officials at the U.S. embassy in Amman, Jordan, and questioned for several hours before he was given a visa.

The British-trained physicist had been "singled out for interrogation" by U.S. officials in Jordan and would not be arriving until the following day, said Iraqi Foreign Minister Naji Sabri in the opening meeting with a U.N. delegation. Iraqi diplomats subsequently told U.N. officials that U.S. officials also offered money to Jaffar and other Iraqi officials in an unsuccessful attempt to persuade them to defect, according to Iraqi and Western diplomats.

The disclosure suggests that Washington may have already begun an aggressive campaign to identify key Iraqi officials for defection several months before U.N. inspectors arrived in Iraq to question Iraq's weapons experts. In recent weeks, the United States has stepped up efforts to encourage new defections, demanding that weapons inspectors invite Iraqi scientists for interviews abroad, where they will be provided with an opportunity to request political asylum.

Information about the alleged defection effort in May came originally from Iraqi officials, who have a stake in portraying the United States as a disruptive force in the inspections process. Still, the Iraqis complained about it at the time -- before the issue became so highly charged -- and U.N. Secretary General Kofi Annan took the claims seriously enough to change the venue of the next round of talks to Vienna.

While the Iraqi claims that the United States had targeted several officials for defection have been generally known, until now their names were unpublicized. In addition to Jaffar, the diplomatic sources said, the Americans also targeted Gen. Amir Saadi, a senior adviser to Iraqi President Saddam Hussein who was also instrumental in developing Iraq's chemical, biological and nuclear weapons programs.

The third individual was Mehdi Labidi, a midlevel technical expert, according to a report Tuesday by the London-based Arab language newspaper Asharq al-Awsat. The newspaper, citing Iraqi officials as sources, reported that U.S. intelligence agents had repeatedly phoned Iraqi officials at their hotels in New York and sought to lure them into defecting with a case filled with cash.

A Bush administration official declined to comment, saying, "We don't comment on intelligence matters." A CIA spokesman declined comment.

The Bush administration, which succeeded in persuading two Iraqi diplomats at Baghdad's U.N. mission to defect in the summer of 2001, has argued that well-placed defectors are the key to unearthing fresh insights into Iraq's secret weapons program. The CIA has a program aimed at encouraging such defections.

But Hans Blix, the chief U.N. weapons inspector, has expressed concern about the United Nations running a defector program. He has said that the United States has yet to come up with ideas for how the international organization can select Iraqi scientists and their families, and take them out of the country for interviews.

The defection of Jaffar would have constituted the most significant intelligence coup on Iraq's weapons program since Hussein Kamel Hassan Majeed, who headed Iraq's secret weapons program, fled Iraq in 1995, prompting the government to hand over millions of pages of secret documents related to its banned weapons program. A former deputy to Hussein Kamel, Jaffar had been at the center of Iraq's secret effort to develop nuclear weapons for more than 20 years. A trusted member of Hussein's inner circle, Jaffar would have likely been a pivotal figure in any recent efforts to restart the program.

"He's extremely significant. He knows more than anybody else, because he is trusted by the top level and he was very involved in all the different programs" in the nuclear field, said David Albright, a former U.N. nuclear weapons inspector who heads the Institute for Science and International Security (ISIS). "He also should have known about all the chemical, biological and missile programs."

The May episode led to an appeal from the Iraqi government to Annan to hold future meetings on weapons inspections in Geneva or Vienna. But the Iraqi government did not go public with the outlines of the story until June, after Washington ordered the expulsion of an Iraqi diplomat in New York -- Abdul Rahman Saad -- on the grounds that he was recruiting U.S. citizens to spy for Iraq.

Iraq's ambassador to the United Nations, Mohammed Douri, told reporters that Washington was simply retaliating because Baghdad had lodged a complaint with the United Nations over U.S. "harassment" of three members of the Iraqi delegation, whom he declined to identify. "This is vengeance," Douri told the Associated Press in June. "They have been asked to stay in the United States -- to defect."

Albright said that Jaffar would have been a natural target for U.S. intelligence agents. A member of Iraq's former royal ruling class, Jaffar was imprisoned and tortured by Hussein until he agreed in the early 1980s to help build the Arab world's first nuclear bomb. But Jaffar also prospered under the regime, increasing his wealth and rising to the post of minister without a portfolio.

"Here's a guy who they tortured to force him to work in the program. I don't see him having a tremendous loyalty to them if he had a choice," Albright said. But "it may be that he is so intertwined financially with the regime, so he has in a sense no way out."

Khidhir Hamza, a former aide to Jaffar who defected to the United States, said that the United States and the United Nations are potentially endangering the lives of Iraqi scientists. Jaffar's flight would have placed his family in peril. The Iraqi regime had responded to previous acts of betrayal mercilessly. After luring Hussein Kamel back to Baghdad, he was gunned down outside his home along with other family members.

Hamza said the International Atomic Energy Agency's efforts to conduct an initial round of interviews with Iraqi scientists in Iraq before narrowing a list of key figures for questioning abroad is particularly dangerous. "Talking to scientists with minders is meaningless; without minders it is an endangerment," he said. "The mere fact that [an individual] is interviewed and chosen will tell the Iraqi government that he is ready to cooperate, and that could endanger him and his family."

That fear has already had a chilling effect on the interviews. One Iraqi scientist, Sabah Abdel-Nour, who participated in Iraq's previous nuclear energy program, told the French press agency that he declined to be interviewed without the presence of an Iraqi official. "The inspectors asked me for a personal interview and proposed that it be in private," he said. "I apologized and asked for the presence of a member of the National Monitoring Directorate."

If Jaffar had any intention of betraying the Iraqi regime, it was anything but evident when he finally arrived in New York for an afternoon meeting with U.N. nuclear experts on May 2. Jaffar complained that his luggage was missing and that he was wearing the same outfit as when he left Baghdad. "He said the [U.S. intelligence] agencies are probably going through every single piece of clothing," according to a U.N. official.

Jaffar then began a tirade, saying the United Nations falsified reports on Iraq's efforts to dismantle its nuclear weapons. "He went ballistic," the official said. "Some people in the meeting thought that he was probably being aggressive with us to show his own government that he had no intention of defecting."

At one point, Mohamed ElBaradei, the director general of the IAEA, threatened to stop the discussions when Jaffar insulted ElBaradei's chief aide, Jacques Baute, the French head of the IAEA's Iraq action team, criticizing his command of English. One U.N. official said Jaffar said, " 'My English is much better than yours, Baute, so don't come play with words in English. Though I must admit that since you married a British national, your English is improving.' "

Another top adviser to Saddam Hussein, Gen. Amir Saadi, may be targeted for defection.