WASHINGTON (CNN) -- The clock begins ticking Tuesday on House Democrats' 100-hour legislative agenda, as lawmakers consider a bill to implement recommendations from the independent commission that investigated the Sept. 11, 2001, terrorist attacks.

To buttress support for the measure, designated as House Resolution 1, House Speaker Nancy Pelosi and her lieutenants handling the legislation appeared Monday with two former Democratic congressman who served on the 9/11 commission, Lee Hamilton and Tim Roemer, who both offered their endorsements.

"If this bill ... is enacted, funded and implemented, then the American people will be safer," said Hamilton, who estimated that about half of the commission's recommendations have not yet been put into place. "We are -- all of us on the 9/11 commission -- deeply pleased that the speaker and the leadership of the House have decided to put this bill forward with the number one designation."

In the run-up to November's midterm election, House Democrats vowed that if they won a majority, they would put the country on a new course by passing six major pieces of legislation, addressing Democratic priorities, in just 100 hours of floor time. The process will begin Tuesday with the 9/11 commission recommendations.

However, the "100 hours" legislation will have to clear the Senate, which operates at a more languid pace, and President Bush could use his veto pen to derail measures he finds objectionable.