WASHINGTON, June 1 - Ahmad Chalabi, the Iraqi leader and former ally of the Bush administration, disclosed to an Iranian official that the United States had broken the secret communications code of Iran's intelligence service, betraying one of Washington's most valuable sources of information about Iran, according to United States intelligence officials.The general charge that Mr. Chalabi provided Iran with critical American intelligence secrets was widely reported last month after the Bush administration cut off financial aid to Mr. Chalabi's organization, the Iraqi National Congress, and American and Iraqi security forces raided his Baghdad headquarters.
The Bush administration, citing national security concerns, asked The New York Times and other news organizations not to publish details of the case. The Times agreed to hold off publication of some specific information that top intelligence officials said would compromise a vital, continuing intelligence operation. The administration withdrew its request on Tuesday, saying information about the code-breaking was starting to appear in news accounts.
Mr. Chalabi and his aides have said he knew of no secret information related to Iran and therefore could not have communicated any intelligence to Tehran.
American officials said that about six weeks ago, Mr. Chalabi told the Baghdad station chief of Iran's Ministry of Intelligence and Security that the United States was reading the communications traffic of the Iranian spy service, one of the most sophisticated in the Middle East.
According to American officials, the Iranian official in Baghdad, possibly not believing Mr. Chalabi's account, sent a cable to Tehran detailing his conversation with Mr. Chalabi, using the broken code. That encrypted cable, intercepted and read by the United States, tipped off American officials to the fact that Mr. Chalabi had betrayed the code-breaking operation, the American officials said.
American officials reported that in the cable to Tehran, the Iranian official recounted how Mr. Chalabi had said that one of "them" - a reference to an American - had revealed the code-breaking operation, the officials said. The Iranian reported that Mr. Chalabi said the American was drunk.
The Iranians sent what American intelligence regarded as a test message, which mentioned a cache of weapons inside Iraq, believing that if the code had been broken, United States military forces would be quickly dispatched to the specified site. But there was no such action.
The account of Mr. Chalabi's actions has been confirmed by several senior American officials, who said the leak contributed to the White House decision to break with him.
It could not be learned exactly how the United States broke the code. But intelligence sources said that in the past, the United States has broken into the embassies of foreign governments, including those of Iran, to steal information, including codes.
The F.B.I. has opened an espionage investigation seeking to determine exactly what information Mr. Chalabi turned over to the Iranians as well as who told Mr. Chalabi that the Iranian code had been broken, government officials said. The inquiry, still in an early phase, is focused on a very small number of people who were close to Mr. Chalabi and also had access to the highly restricted information about the Iran code.
Some of the people the F.B.I. expects to interview are civilians at the Pentagon who were among Mr. Chalabi's strongest supporters and served as his main point of contact with the government, the officials said. So far, no one has been accused of any wrongdoing.
In a television interview on May 23, Mr. Chalabi said on CNN's "Late Edition" that he met in Tehran in December with the Iranian supreme leader, Ayatollah Ali Khamenei, and the Iranian president, Mohammad Khatami. He also said he had met with Iran's minister of information.
Mr. Chalabi attacked the C.I.A. and the director of central intelligence, George J. Tenet, saying the agency was behind what Mr. Chalabi asserted was an effort to smear him.