Former New Jersey Gov. Thomas Kean, new chairman of the commission investigating the Sept. 11 attacks, promised a bipartisan and thorough investigation to determine why the attacks weren't prevented.

President Bush appointed Kean on Monday, turning to a moderate Republican with a record of cooperation with Democrats to replace Henry Kissinger as chairman of the 10-member National Commission on Terrorist Attacks.

Kean, appearing Tuesday on NBC's Today program, promised an aggressive investigation.

"We have the power to subpoena. It's really a remarkably broad mandate,'' he said, "so I don't think we'll have any problem looking under every rock.''

"I've got no problems in going as far as we have to in finding out the facts,'' Kean said.

Also Monday, Senate Republican leader Trent Lott filled the panel's last member with John Lehman, Navy secretary during the Reagan administration.

Kissinger, secretary of state under Presidents Nixon and Ford, resigned Friday because of criticism over possible conflicts of interest that he said would have forced him to give up his consulting firm.

Relatives of Sept. 11 victims said their support of Kean and his panel will depend on its political independence and whether commissioners have business conflicts that could affect their work.

The commission, comprising five Democrats and five Republicans, will investigate issues related to the attacks, including intelligence, aviation security and immigration. It is expected to begin work next month.

Kean, 67, is president of Drew University in Madison, N.J., about 30 miles from New York City. He was New Jersey's governor from 1982 to 1990.

At a news conference Monday, Kean said he only learned of the appointment the night before. "I feel like a ton of bricks fell on me,'' he said.

"The only instructions I got from the White House is to do the best job I could and to be bipartisan,'' he said.

In a statement, Bush praised Kean's "integrity, fairness and good judgment'' and said: "It is important that we uncover every detail and learn every lesson of Sept. 11.''

Victims' relatives and some lawmakers have been skeptical about Bush's commitment to the investigation. Bush initially opposed the panel and later insisted on limitations to its subpoena authority. Both sides accused the other of trying to manipulate the panel for political purposes. The final report is due less than six months before the 2004 elections.

Stephen Push of the advocacy group Families of September 11, said he was optimistic about the panel's independence. But he and other leaders of Sept. 11 organizations said they wanted to learn more about the commissioners' business dealings.

"Let's make sure everybody passes the conflicts test,'' said Kristen Breitweiser, a leader of September 11 Advocates.

Breitweiser's husband, Ronald, a senior vice president of Fiduciary Trust International, was among 87 employees of the financial company who died at the World Trade Center. Kean has long served as a director of Fiduciary Trust.

Kean also served on the board of Aramark Corp., which manages food and support services at office buildings and other facilities. Aramark ran the food court on top of 2 World Trade Center as well as concessions and tours of the observation deck. Several of its employees died in the tower.

Besides Kissinger, the panel's original vice chairman, former Sen. George Mitchell, also resigned last week, partly because of objections raised about potential conflicts. Mitchell was replaced by former Rep. Lee Hamilton, D-Ind.

Kean said he does not see any potential conflicts of interest and will make any financial disclosure required.

He said the commission will be an opportunity for the country to draw together.

"I lost a number of good friends on 9-11. So did a lot of us in this area,'' he said. "At this point in time the country needs to come together.''

Kean is a moderate Republican, liberal on many social issues, who has often been comfortable working with Democrats. He wrote a 1988 book titled "Politics of Inclusion."