Sens. Joseph Lieberman, D-Conn., and John McCain, R-Ariz., said the 14-member commission would be based on the panels that investigated the attack on Pearl Harbor in the 1940s and the assassination of President Kennedy in the 1960s.
"To prevent further tragedies, we need to know how an attack could have happened," McCain said at a press conference to introduce legislation creating the commission.
The pair said the National Commission on Terrorist Attacks Upon the United States would "make a full and complete accounting of the circumstances surrounding the attacks" and the extent of the country's "preparedness for, and response to, the attacks."
To accomplish that goal, the senators said, the commission would have far-reaching powers and deep pockets: It would hire top-level staff, and investigators would have the power to subpoena witnesses. Members could hold closed-door hearings when necessary.
However, Lieberman and McCain said they hoped that the panel would perform much of its work in the public eye.
"We need public hearings," McCain said. "That's the way to restore public confidence."
McCain and Lieberman said the commission would have power to pursue a variety of possible causes of the attacks, from intelligence lapses to diplomatic failures. The panel also would be free to investigate the subsequent anthrax scare.
Of the commission's 14 members, 10 would be appointed by the chairmen of congressional committees and four by the President. The White House would appoint the chairman of the panel.
Separately, House Democrats unveiled a $24 billion homeland security package Thursday, just hours after the House approved $8.5 billion for public health, infrastructure and law enforcement.
Democrats said a package approved by the House and later endorsed by the Senate falls short of the nation's needs for homeland security spending.
Rep. Robert Menendez, D-N.J., who wrote the bill, said the new spending would not threaten other projects, because it would be paid for by suspending income-tax rate cuts for the top three brackets until 2007.