WASHINGTON – President Bush yesterday nominated a former aggressive New York City prosecutor and sitting federal court judge, Michael Chertoff, to lead the Department of Homeland Security.

Judge Chertoff headed federal criminal prosecutions at the time of the September 11, 2001, attacks and became a key architect of the government’s legal response to terrorism. The president credited him with helping trace the terrorist attacks to the Al Qaeda network, and with improving intelligence sharing within the FBI and among state and local officials.

“He understood immediately that the strategy on the war on terror is to prevent attacks before they occur,” Mr. Bush said.

Judge Chertoff also served as a top lawyer to the Senate committee that questioned Senator Clinton in connection with the Whitewater Arkansas land deal.

While senators from both parties praised the nominee, whom Mr. Bush called a “key leader in the war on terror” and a man of “energy and intellect,” Mrs. Clinton’s response to Judge Chertoff’s nomination was more tepid.

She said in a statement yesterday that his nomination “merits careful consideration.”

“I look forward to meeting with Judge Chertoff in the very near future to discuss many important issues, including the specific homeland security needs of New York as well as the many homeland security challenges confronting our nation,” she said.

Mrs. Clinton was the only senator from either party to vote against Judge Chertoff’s confirmation to the 3rd Circuit Court of Appeals in 2003, and she was alone in voting against his appointment as assistant attorney general in 2001.

The 51-year-old native of Elizabeth, N.J., cut his prosecutorial teeth going after organized crime in the U.S. Attorney’s office under Rudolph Giuliani in the early 1980s. He rose to become the top prosecutor in New Jersey, and later in the federal Justice Department.

He has fought against racial profiling and favored trying terror suspects in civilian courts rather than military tribunals, but he has also drawn criticism for allowing the lengthy detention of noncitizens without access to lawyers, and for pushing the expansion of FBI investigative powers.

Judge Chertoff led the aggressive prosecution of Zacharias Moussaoui, the only person charged in connection with the terrorist attacks, and he oversaw the prosecution of the “American Taliban” member, John Walker Lindh.

Mr. Bush noted that the judge has already been confirmed three times by the Senate, and early reactions suggested a fourth confirmation is likely.

Senator Schumer called the judge a “strong choice” who “has the resume to be an excellent Homeland Security secretary, given his law enforcement background and understanding of New York’s and America’s neglected homeland security needs.”

Mr. Schumer said he had already spoken with the judge and pressed him on homeland security funds. Judge Chertoff’s reaction was “receptive, though noncommittal,” and the two agreed to “discuss New York’s homeland security priorities in the near future,” Mr. Schumer said.

After the Whitewater hearings, Judge Chertoff campaigned on behalf of Senator Dole in his unsuccessful presidential campaign against President Clinton.

In the 2000 election, Judge Chertoff was vice chairman of the Mr. Bush’s campaign in the state of New Jersey, and he has contributed to various Republican campaigns.

Rep. Carolyn Maloney, a New York Democrat who chairs the House Democratic Task Force on Homeland Security, said she was concerned about his political past.

“The nomination of a figure who was so partisan in the 1990s leaves some doubt that he will be able or willing to work with Democrats on our ideas for better national security,” Ms. Maloney said.

The selection of Judge Chertoff came as a surprise to many observers, in part because of the rarity of a federal judge giving up a lifetime appointment.

“He is giving up a lifetime judgeship to run a department which has a tremendous amount of bureaucratic problems, so he must really want the job,” said Rep. Peter King, a Republican of Long Island, who sits on the House Homeland Security Committee.

The White House spokesman, Scott McClellan, said the judge’s name had been on the administration’s short list all along, but officials had assumed that since he had been on the court since 2003, he would have preferred to stay on the bench.

“That assumption was wrong,” Mr. McClellan said yesterday.

Mr. Bush met with Judge Chertoff at the White House Sunday and offered him the position Monday morning, Mr. McClellan said.

In introducing Judge Chertoff, Mr. Bush emphasized that he “has helped to protect his fellow Americans while protecting their civil liberties.”

Calling the judge a “strong and decent man,” the president noted that Judge Chertoff had stood against racial profiling and worked with the NAACP Legal Defense Fund to represent poor inmates on death row.

Judge Chertoff has won bipartisan praise for his pro bono work for a New Jersey State Senate committee that attempted to unseat a former state attorney general, Peter Verniero, from the state’s Supreme Court for allegedly sanctioning and covering up racial profiling by law enforcement.

At the time of his judicial confirmation, a group that opposes many Bush appointees, the Alliance for Justice, praised him as “an independent thinker, at least on certain civil justice issues.”

The group noted that he had praised a Supreme Court decision striking down a Texas anti-sodomy statute. “The sex lives of adult Americans, like their religion, is none of the government’s business,” he wrote in a commentary on the decision.

But the American Civil Liberties Union yesterday expressed concern about Judge Chertoff’s involvement in the administration’s terrorism policies, particularly his role in holding noncitizens for long periods after the September 11, 2001, terrorist attacks without bail or access to lawyers.

“We are troubled that his public record suggests he sees the Bill of Rights as an obstacle to national security, rather than as a guidebook for how to do security properly,” said the ACLU’s chief legislative counsel, Gregory Nojeim.

Citing Judge Chertoff’s involvement in allowing the FBI to infiltrate religious and political gatherings, and to eavesdrop on previously confidential attorney-client conversations in prisons, they called for “aggressive” questioning at his hearing.

Mr. King downplayed such concerns. “That’s the reason I support him. He realizes that we are at war and it is a time to be tough. He has a constitutional but tough attitude toward domestic terrorism,” Mr. King said.

From 1983 to 1987, Judge Chertoff was an assistant U.S. attorney general to Rudolph Giuliani, who ran that office. While Mr. Chertoff was only in his mid-30s, Mr. Giuliani entrusted him to lead the prosecution of several mafia leaders, in what he called “the commission of La Cosa Nostra.”

Another alumna of that office, Frances Townsend, will remain as the president’s Homeland Security adviser, the White House said yesterday.

Judge Chertoff’s nomination came after Mr. Bush’s first choice, a close associate of Mr. Giuliani and a former police commissioner, Bernard Kerik, withdrew his name from consideration after numerous ethical questions were raised about his personal life and business deals.

Mr. Giuliani called the president’s choice of Judge Chertoff “superb.”

A New York litigator and former deputy mayor, Randy Mastro, who worked with Judge Chertoff in the U.S Attorney’s Office, called him “monster smart.”

“He is very focused, very dedicated, incredibly creative, and tireless when he focuses on an objective,” Mr. Mastro said.

A graduate of Harvard College and Harvard Law School, where he edited the Harvard Law Review, Judge Chertoff was a law clerk to Supreme Court Justice William Brennan.

Prior to his court appointment, he was a partner in the law firm of Latham and Watkins, where he chaired the firm’s white-collar crime practice.

In accepting the nomination, Judge Chertoff praised first responders as well as the outgoing secretary, Thomas Ridge, and promised to protect individual rights.

“If confirmed, I pledge to devote all my energy to promoting our homeland security, and as important, to preserving our fundamental liberties,” Judge Chertoff said.