The White House has told lawmakers that former Secretary of State Henry Kissinger, President Bush's choice to head a commission investigating the Sept. 11 attacks, is not required by law to disclose his business clients.

Senate Democrats want the list to determine whether Kissinger's clients pose conflicts of interests.

A White House official, speaking on condition of anonymity, said federal law guiding presidential appointments does not require such disclosures when the appointee is not paid. Kissinger is drawing no salary.

Senate Democrats claim all 10 members of the commission are required to submit financial disclosures, which would include naming clients. That opinion was supported by a report issued last week by Congress' research arm, the Congressional Research Service.

The White House position wouldn't prohibit Kissinger from turning over the client list on his own. The former secretary of state was not immediately available for comment.

The confrontation came to a head as former Sen. George Mitchell resigned from the commission.

Former Rep. Lee Hamilton, D-Ind., will replace Mitchell as vice chairman of the National Commission on Terrorist Attacks.

The commission will follow up the work of the congressional inquiry that issued its final report Wednesday on intelligence failures leading up the terrorist attacks. The commission will conduct a broader investigation, looking at issues beyond intelligence, including aviation security and immigration.

In a letter to congressional Democratic leaders Wednesday, Mitchell said he had understood that the commission work would be part time.

"However, as you know, some have urged that I sever all ties to the law firm with which I am associated," he wrote. "Since I must work to support my family, I cannot comply."

He said concerns were raised about potential conflicts of interests and whether he would devote the time necessary to the commission. Some politicians and commentators have raised similar questions about Kissinger, who leads a major consulting firm.

Mitchell said his legal work would not have posed a conflict, but he was concerned about how much time the commission would have demanded.

His replacement, Hamilton, served more than 30 years in the House and is a former chairman of the International Relations and Intelligence committees.

The commission will be made up of five Democrats and five Republicans, including Kissinger, who was appointed by President Bush.

Democratic leaders on Wednesday appointed four other members to the panel: outgoing Sen. Max Cleland, D-Ga., outgoing Rep. Timothy Roemer, D-Ind., attorney Richard Ben-Veniste, and Jamie Gorelick, a deputy attorney general in the Clinton administration.

On Tuesday, Senate Republican leader Trent Lott appointed former Sen. Slade Gorton, R-Wash. Republican congressional leaders will name three more members.

Gorton's appointment has disappointed some relatives of the Sept. 11 victims. Gorton, a former chairman of a Senate aviation subcommittee, had close ties with Boeing Co., the largest private employer in Washington state. Boeing made all four planes used in the attacks.

Gorton's law firm, Seattle-based Preston Gates Ellis, also represents several major airlines.

"I think Gorton is a terrible appointment," said Stephen Push, whose wife, Lisa Raines, died in the attack on the Pentagon.

Kristen Breitweiser, whose husband Ronald was killed in the World Trade Center, said Gorton's appointment follows a troubling pattern set by the selection of Kissinger. Family members have criticized Kissinger's appointment because of potential conflicts.

"We want this commission to be independent -- to fix problems that became apparent Sept. 11," said Breitweiser, of Middletown, N.J.

Gorton did not return messages left at his offices in Seattle and Washington.

Push and Breitweiser said family members also want Lott to appoint former New Hampshire Sen. Warren Rudman to the panel. Rudman served on an advisory group that warned of U.S. vulnerability to terrorist attacks before Sept. 11, 2001.