WASHINGTON – The secretary of Homeland Security, Tom Ridge, who oversaw the creation of the largest new federal department in half a century, announced yesterday that he is resigning from President Bush’s Cabinet. Several New Yorkers have been among the top names mentioned as likely candidates to take his place.

After almost three intense years of welding together 22 disparate agencies and 180,000 federal workers into a single entity responsible for everything from screening immigrants to stockpiling vaccines against biological attack, the 59-year-old said he was stepping down to spend more time with his family.

A former governor of Pennsylvania and a trusted friend of the president, Mr. Ridge faced bureaucratic turf wars while contending with domestic terrorist threats as America invaded Afghanistan and Iraq and held the first presidential elections since the attacks of September 11, 2001.

Despite enduring occasional ridicule for instituting color-coded terror alerts and instructing Americans to stock up on duct tape, his tenure was free of domestic terrorist incidents.

At a press conference yesterday, Mr. Ridge noted that the nationwide threat level had not been raised in almost a year.

Mr. Ridge said he could not prove that the measures taken by his department, with a 2005 budget of $28.9 billion, had prevented terrorist attacks. But he said he was “fairly confident” that the changes made “curb to cockpit” in airport security and in maritime security had deterred potential plots.

Mr. Ridge submitted a formal resignation letter to the president yesterday, writing that he would stay until February 1 or earlier, if the Senate confirms a successor.

He said he had “accomplished a great deal in a short period of time,” but told the president “there will always be more work for us to do in homeland security.”

His successor will face the challenge of coordinating the activities of federal, state, and local authorities, as well as the private sector, which he has estimated controls 85% of the nation’s critical infrastructure. “Homeland Security has never been to me just a department,” Mr. Ridge said. “It’s about the integration of a country.”

Mr. Ridge said his successor would face the “enormous challenge and great opportunity” of keeping the country safe while respecting the Constitution and working with state, local, and international governments.

The list of likely successors includes a former city police commissioner, Bernard Kerik, who oversaw training of police in Iraq, and a Long Island-born lawyer, Frances Townsend, who serves as the president’s homeland security adviser.

Governor Pataki and a former mayor, Rudolph Giuliani, have been frequently mentioned, but have both said they are not interested in the job.

Another possible successor is the undersecretary for border and transportation security in the Homeland Security Department, Asa Hutchinson.

New York politicians yesterday praised Mr. Ridge’s performance in a demanding role, but said they hoped Mr. Ridge’s successor would secure more federal funding for security upgrades around the country, and especially in New York City, which has received less funding per capita than some rural states.

Senator Schumer called Mr. Ridge a decent man and a fine public servant who “was not given the leeway or resources to tighten up homeland security the way it should be done.”

A member of the House Homeland Security Committee, Rep. Peter King, a Republican of Long Island, said Mr. Ridge did “a very good job” of creating a new department, but hoped his successor would “do all that can be done to get the homeland security funding to where it’s needed, like New York City, by fighting for it in Congress and pushing for it in the budget.”

The next secretary should also take a hands-on approach to integrating agencies, he said. “I think the successor should be aggressive, the type of person who crashes down doors and is involved with the local police and the joint terrorism task forces, getting the job done on the ground,” Mr. King said.

The chairwoman of the House Democratic Task Force on Homeland Security, Rep. Carolyn Maloney of New York, called the secretary an “upstanding man” who did his best in an important and intense role.

“I will remember his tenure as one of sensible rhetoric that, unfortunately, was not matched with substance. That is an indictment of the Bush administration’s backward ideas about security, not Tom Ridge the man,” Ms. Maloney said.

After 22 years in public service, Mr. Ridge said he had not yet decided his next career move, saying only, “I’m going to step back a little bit, breathe deeply and then decide.”

He said he was looking forward to raising “family matters to a higher priority,” and to attending the rugby games of his son, Tommy, a college student.

While governor, he said he was able to coach his daughter Lesley’s softball team, something that would be impossible in his current job.

A Harvard graduate and decorated Vietnam veteran who served as an infantry staff sergeant in the Army, Mr. Ridge was the first enlisted man to serve in Congress, to which he was first elected in 1982. He was serving his second term as the governor of Pennsylvania when he was tapped by Mr. Bush to spearhead the creation of the new department in October 2001.

The Bush administration originally opposed the creation of a Cabinet-level agency, and Mr. Ridge’s original job title was director of the Office of Homeland Security. But in the face of criticism that the job required greater authority and resources, the administration relented and, in January 2003, Mr. Ridge was given a full secretary position and put in charge of the government department he has described as having “as many divisions as GE and as many employees as Federal Express.”

He compared the ordeal of merging the agencies, with their various hierarchies, computer networks, and payroll systems, to a “full-scale divestiture, merger, acquisition and start-up all coming together at once.”

Mr. Ridge fought the perception that internal turf wars and logistical challenges distracted the department from its job of enhancing homeland security, and slowed the delivery of federal grants to state and local governments.

But yesterday he admitted that, for example, the merging of the customs and immigration control agencies into a single entity had been “difficult,” and conceded that there “might be some people out there that are still a little uncomfortable with it.” But, he said, the department is successfully “working through” such “irritants.”