Unrelenting in their criticism of Ahmad Chalabi (search), lawmakers pledged to investigate charges that the Iraqi National Congress (search) leader passed classified information to Iran (search).

Sens. Dianne Feinstein (search), D-Calif., and Chuck Hagel (search), R-Neb., both members of the Senate Intelligence Committee, said they would ask the intelligence agencies for a report on the allegations.

"This is a very, very serious charge," Hagel said in a televised interview. "There is no way the Senate Intelligence Committee is not going to be in this."

Chalabi, a member of the Shiite Islamic sect to which the majority of Iranians and Iraqis belong, once was a favorite of Pentagon officials. He recently came under suspicion that he might have handed over sensitive information to Iran about the U.S. occupation.

He had provided intelligence to the Bush administration about weapons of mass destruction, which was used to justify the U.S. war against Iraq, but Chalabi's information came under major criticism after no weapons were found.

On Sunday, Chalabi called the spying charges false, the alleged activities nonexistent. He said CIA director George Tenet (search) was spreading the allegations to discredit him.

"I'm prepared to go to Congress and testify under oath and expose all the information and the documents in our possession, and let George Tenet come himself to Congress to testify," Chalabi said on ABC's "This Week."

Chalabi said he never provided false information about weapons of mass destruction but simply provided to the CIA three defectors who were believed to have had critical information.

"It is not our responsibility to verify this information," Chalabi said in a televised interview. "It is blame-shifting, again, by the CIA."

An intelligence official, who spoke on condition of anonymity, said the agency would welcome Chalabi's testimony as a "positive development." CIA spokeswoman Anya Guilsher would not comment on the matter.

Sen. Evan Bayh, D-Ind., also a member of the Intelligence Committee, said he wasn't particularly interested in hearing Chalabi testify. "I think the American people are verging upon hearing fatigue," he said on ABC's "This Week."

Some lawmakers criticized Chalabi Sunday as a self-promoter who duped the United States into providing $340,000-a-month payments for his intelligence information.

The government recently stopped the payments.

"I think [Chalabi's] a charlatan. I think he's a manipulator," Feinstein said. "He has tremendous personal motives for his own empowerment. And I think the fact that we fell victim to these manipulations is unfortunate."

Hagel said both the Clinton and Bush administrations should have heeded warning signs about Chalabi's credibility, including a 1992 conviction in Jordan in a banking scandal. The Iraqi contends the conviction resulted from misconduct by Jordanian authorities and the now-deposed Saddam Hussein government in Baghdad.

"I had big concerns about him," Hagel said. "There were a number of us who warned this administration about him. ... But the fact is, there were some in this administration, some in Congress who were quite taken with him."

Sen. Pat Roberts, R-Kan., chairman of the Senate Intelligence Committee, stopped short of calling Chalabi a "con man."

He noted, however, that his committee's coming report on prewar assessments in Iraq, set to be released next month, will include criticism of Chalabi.

"There is a school of thought, especially by the CIA, that Mr. Chalabi's intelligence input was not that good, and that's probably an understatement," Roberts said on "Face the Nation."