Richard A. Clarke, the blunt, sometimes abrasive White House adviser who raised the alarm about unconventional national security threatsranging from failed states to biological and computer terrorism for more than a decade, quietly resigned as President Bush's cybersecurity chief on Friday.

In an interview after his last day in office, Mr. Clarke warned that although the government had made considerable progress in defending its electronic infrastructure from computer attacks, the United States faced ever greater peril, given its growing dependence on the Internet.

"A sophisticated cyberattack may not result in massive deaths," he said. "But it could really hurt our economy and diminish our ability to respond to a crisis, especially if it is combined with a war, or a terrorist attack."

Mr. Clarke said the attack last weekend by a computer bug known as the Sapphire worm showed the vulnerability of America's increasingly Internet-based economy. Though it was a relatively simple bug, he said, Sapphire, which has also been called Slammer, ravaged systems throughout the United States and overseas in just a few hours, shutting down some of the Bank of America's automated teller machines and Continental Airlines' online ticketing system, and denying access to the Internet to millions of personal computer owners.

"Don't assume that the damage done by hackers in the past is predictive of the future," Mr. Clarke said. "As Sept. 11 showed, as long as our vulnerabilities are large, some enemy will exploit them in a new and hugely damaging way."

Before tackling the country's computer vulnerabilities, Mr. Clarke was in charge of the White House's counterterrorism office for President Bush and President Bill Clinton. He sometimes antagonizes officials in federal agencies and even some White House colleagues by demanding more aggressive action against Islamic extremists like Osama bin Laden. Mr. Clarke, associates said, was an ardent proponent of military action not only against Mr. bin Laden, but also against the Taliban government of Afghanistan, which provided a home for him and his terrorist network, Al Qaeda.

After the Sept. 11 attacks, colleagues said, he played a critical role in the White House situation room, helping to ground the nation's airliners and to increase security at other vulnerable targets.

Mr. Clarke said the nation is safer today than before Sept. 11 because Al Qaeda's sanctuary in Afghanistan is gone and because Americans had rounded up hundreds of Qaeda operatives abroad and tightened aviation security overseas and domestically. "But we still don't have control of our borders, or sufficient control of terrorist money transfers," he said. "And we still don't know where all the potential sleeper cells are in the U.S."

At the same time, he said, he feared that civil rights might be eroding in the struggle against terrorism. "When we sacrifice our civil liberties and privacy rights, the terrorists win because they have gotten us to change the nature of our country," he said. Despite having fought terrorism for more than 11 years, he said, "I have never seen one reason to infringe on privacy or civil liberties."

Mr. Clarke said he was leaving his post now because "11 years in the White House and a total of 30 in government is more than enough," and because President Bush would soon unveil a new national strategy to protect the nation's information infrastructure, which Mr. Clarke and his team had drafted.

Associates said Mr. Clarke was becoming increasingly weary of battling a federal bureaucracy that was resistant to considering new issues like cyberterrorism as real threats.

Mr. Clarke dismissed reports that his bureaucratic opponents had blocked him from being offered a senior post in the new Department of Homeland Security.

In a recent book, Anthony Lake, a national security adviser to President Clinton, called Mr. Clarke "a bulldog of a bureaucrat" and noted that his "bluntness toward those at his level" had not earned him "universal affection."

Mr. Clarke once said: "This was not a popularity contest. When you are working on life-and-death issues, you sometimes have to bring out the bulldozer."