WASHINGTON, June 2 - Federal investigators have begun administering polygraph examinations to civilian employees at the Pentagon to determine who may have disclosed highly classified intelligence to Ahmad Chalabi, the Iraqi who authorities suspect turned the information over to Iran, government officials said Wednesday.The polygraph examinations, which are being conducted by the Federal Bureau of Investigation, are focused initially on a small number of Pentagon employees who had access to the information that was compromised. American intelligence officials have said that Mr. Chalabi informed Iran that the United States had broken the secret codes used by Iranian intelligence to transmit confidential messages to posts around the world.
Mr. Chalabi has denied the charge. On Wednesday, his lawyers made public a letter they said they had sent to Attorney General John Ashcroft and F.B.I. Director Robert S. Mueller III repeating Mr. Chalabi's denials and demanding that the Justice Department investigate the disclosure of the accusations against Mr. Chalabi.
The lawyers, John J. E. Markham II and Collette C. Goodman, said in the letter, "The charges made against Dr. Chalabi - both the general and the specific ones are false."
They also said, "We ask that you undertake an immediate investigation to find and hold accountable those who are responsible for these false leaks."
Officials would not identify who has taken polygraph examinations or even who has been interviewed by F.B.I. counterespionage agents. It could not be determined whether anyone has declined to submit to a polygraph test.
No one has been charged with any wrongdoing or identified as a suspect, but officials familiar with the investigation say that they are working through a list of people and are likely to interview senior Pentagon officials.
The F.B.I. is looking at officials who both knew of the code-breaking operation and had dealings with Mr. Chalabi, either in Washington or Baghdad, the government officials said. Information about code-breaking work is considered among the most confidential material in the government and is handled under tight security and with very limited access.
But a wider circle of officials could have inferred from intelligence reports about Iran that the United States had access to the internal communications of Iran's spy service, intelligence officials said. That may make it difficult to identify the source of any leak.
Government officials say they started the investigation of Pentagon officials after learning that Mr. Chalabi had told the Baghdad station chief of Iran's intelligence service that the United States was reading their communications. Mr. Chalabi, American officials say, gave the information to the Iranians about six weeks ago, apparently because he wanted to ensure that his secret conversations with the Iranians were not revealed to the Americans.
But the Iranian official apparently did not immediately believe Mr. Chalabi, because he sent a cable back to Tehran detailing his conversation with Mr. Chalabi, American officials said. That cable was intercepted and read by the United States, the officials said.
Mr. Chalabi and his supporters argue that the accusations against him are part of a C.I.A.-inspired campaign to discredit him. His backers have been dismayed that the Bush administration recently divorced itself from Mr. Chalabi and his group, the Iraqi National Congress. They contend that the move was instigated by the C.I.A., which they say is now wielding intercepted Iranian communications as a weapon against Mr. Chalabi.
Richard N. Perle, the former chairman of the Defense Policy Board and an influential Chalabi supporter, said Wednesday that the notion that Mr. Chalabi would compromise the American code-breaking operation "doesn't pass the laugh test." Mr. Perle said it was more plausible that the Iranians, knowing already that the United States was reading its communications, planted the damning information about Mr. Chalabi to persuade Washington to distance itself from Mr. Chalabi.