Former Secretary of State Henry Kissinger stepped down Friday as chairman of a panel investigating the Sept. 11 attacks, citing controversy over potential conflicts of interest with his private-sector clients.

In a letter to President Bush released by the White House, Kissinger said that while specific conflicts might have been resolved, satisfying all concerns would have "significantly delayed" the commission's work.

"I have, therefore, concluded that I cannot accept the responsibility you proposed."

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The decision was another blow for the fledging panel and the families of Sept. 11 victims. The panel's original vice chairman, George Mitchell, resigned from the commission Wednesday, partly because of pressures to quit his law firm.

Kissinger's resignation came one day after he tried to assure victims that his business interests would not conflict with his duties as chairman. The White House and congressional Democrats had clashed on whether he had to disclose his business clients, with Mr. Bush's advisers saying the law did not require such disclosures.

Mr. Bush issued a written statement saying he accepted Kissinger's resignation with regret. "His chairmanship would have provided the insights and analysis the government needs to understand the methods of our enemies and the nature of the threats we face," the statement said.

The president promised to pick a new chairman to help "uncover every detail and learn every lesson of Sept. 11, even as we act on what we have learned so far to better protect and defend America."

Kissinger said he had told White House lawyers he was willing to remove the appearance of conflict of interests by submitting "all relevant financial information" to the White House and to an independent review. He said he could not liquidate Kissinger Associates, his international consulting firm, without delaying the commission's work.

It was not immediately clear who, if anybody, asked him to liquidate his firm.

"My hope is that by the decision to step aside now, the Joint Commission can proceed without further controversy," he said.

The commission will investigate events surrounding the attacks, examining issues including aviation security, immigration and U.S. diplomacy. It will build on a congressional inquiry, completed this week, into intelligence failures.

Senate Democrats say all commission members, including Kissinger, must submit financial disclosures that would reveal potential conflicts. That view was supported by a report issued last week by Congress' research arm, the Congressional Research Service.

But the White House contends Kissinger, as Bush's sole appointee, need not submit a report. It says federal law does not require presidential appointees to submit disclosures if they are not drawing salaries, as is the case with Kissinger.

But a second Congressional Research Service report said all members of the commission — including a presidential appointee — would be bound by Senate ethics requirements. That report was released Thursday by the office of Sen. Joe Lieberman, D-Conn., chairman of the Senate Governmental Affairs Committee.

The dispute is the latest involving the commission that will begin its work early next month. Family members and congressional Democrats have questioned whether the Bush administration wants an honest evaluation of the attacks, with its report due to come out less than six months before the 2004 presidential election.

Negotiations creating the commission were bogged down by disputes over its makeup and rules, with lawmakers and the White House accusing each other of trying to manipulate it for political purposes.

