The Homeland Security Department combines the forces of 22 agencies and 170,000 workers who patrol America's borders, secure computer networks, check for contamination of crops and otherwise help guard against terrorism. Saturday is its first full day of work.
"Every member of this new department accepts an essential mission — to prevent another terrorist attack," Mr. Bush told Cabinet members and federal workers involved in homeland defense. "Yours is a vital and important step in reorganizing the government to meet the threats of a new era as we continue to work to secure this country."
On Saturday, the agencies and workers officially fold into the new department, the largest government reorganization since the Defense Department was created in 1947.
Tom Ridge, Mr. Bush's 15th Cabinet secretary, leads the agency.
Some Democrats, including the party's presidential candidates, have complained that the Bush administration hasn't devoted enough money and resources to the job.
In response, Mr. Bush said much has been done already.
While there is no guarantee of preventing an attack, the president said, "We're determined to do everything in our power to defeat this enemy and defend our people" while upholding the Constitution.
Most of the department's workers, spread across the nation, will continue to show up for work at the same office, ship or airport as before. Only about 10 percent — or 17,000 — work in the Washington area, and about 1,000 of them will work from the department's headquarters. It's located at least temporarily at a secure office complex run by the Navy.
The president created a homeland security office inside the White House after the Sept. 11, 2001, attacks and tapped Ridge, then Pennsylvania governor.
Mr. Bush initially resisted Democratic proposals for a Cabinet-level agency. But once he endorsed it, the president pushed Congress for fast action as it debated such issues as whistle-blower protections, concerns over civil liberties and collective bargaining for department employees.
The department combines agencies that are also responsible for a range of duties besides combatting terrorism, such as collecting tariffs, rescuing boaters and watching for outbreaks of common livestock diseases.
The Homeland Security Department will have its own analytical unit to examine intelligence gathered by the CIA, FBI and others for clues about terrorist plots. It also will coordinate with 2 million police, firefighters, medical personnel and other emergency workers around the nation.
Among the agencies it will take over are the Secret Service, Coast Guard, Immigration and Naturalization Service, Customs Service and the Transportation Security Administration. The first-year budget is expected to be about $33 billion.