When CIA Director George J. Tenet issued a warning in December 1998 that "we are at war" with al Qaeda, one of his colleagues faxed it to the heads of other major intelligence agencies. But none of them acted on it, and several did not remember seeing it until after the terrorist attacks of Sept. 11, 2001.

In 2000, as part of his effort to bring more resources to bear on the al Qaeda threat, Tenet asked an official in the agency's counterterrorism center to figure out how to improve al Qaeda analyses. But the center never anticipated an attack by aircraft, and the specialist it hired at Tenet's urging reported for work one day before the attack occurred.

These two anecdotes, both divulged by the presidential commission investigating the Sept. 11 assaults, illustrate what some experts depict as the mixed record of Tenet's tenure as director of the CIA, a job he said yesterday he will quit in July.

On one hand, Tenet is credited with sounding the alarm about the most critical threat to U.S. security in the post-Cold War era: Osama bin Laden and his adherents and allies. But he was unable to convince others in the administration of its urgency, and he was unable -- in time to catch the terrorists -- to forge links between intelligence agencies that would have put critical information in investigators' hands.

"We made mistakes," he told the commission on April 14, in one of the few such public remarks by any senior administration official.

At the same time, Tenet has told friends that he is proud of his agency's collection of intelligence on Libya's weapons programs, which persuaded that nation's leader, Moammar Gaddafi, to dismantle his nuclear, chemical and biological programs. He also oversaw a worldwide probe of international sales of nuclear equipment that enabled the United States to persuade Pakistan to stop exports by its leading scientist, Abdul Qadeer Khan.

Recently, Tenet has been in the thick of controversy over the quality of his agency's prewar intelligence on Iraq, particularly on its chemical, biological and nuclear weapons programs. Three months ago, he said "we may have overestimated the progress Saddam [Hussein] was making" on nuclear weapons, and acknowledged that his prediction that Iraq had chemical arms remains unproved.

Tenet, who was appointed in 1997 to one of Washington's most sensitive jobs, at a place where secrecy shrouds most successes but notoriety attends every mistake, survived longer than all of his predecessors in the job except one, Allen W. Dulles, who was fired in 1961 after the CIA's abortive incursion at the Bay of Pigs in Cuba.

The job is a lightning rod for criticism, whenever foreign policy goes awry or mistakes are made by intelligence officials outside of the CIA's control. Capitol Hill "typically holds George responsible" even though the Pentagon actually controls the bulk of the U.S. intelligence community, said Bob Kerrey (D-Neb.), a former vice chairman of the Senate intelligence committee who now sits on the Sept. 11 commission.

"George is being scapegoated as the guy who had bad intelligence," Kerrey said, because the administration was determined -- in Kerrey's opinion -- to wage war with Iraq no matter what.

For the past year, Tenet has kept a football helmet on his desk, a gift from University of Oklahoma Coach Bob Stoops as the U.S. conflict in Iraq wound down and controversy began to swirl around Tenet -- principally because of the government's inability to find expected weapons of mass destruction in Iraq. Tenet told friends last year the job was wearing him down, and they said yesterday that his decision came as no surprise.

The agency Tenet is leaving is far different from the one he took over. At that time, only a few dozen officers were training to join its clandestine service, which has the difficult task of recruiting agents in hostile countries. The foreign-language expertise of many of its employees lay mostly in languages pivotal to the Cold War, rather than the developing or failed states that now give rise to most modern conflicts. A scandal involving the agency's links to thugs in Guatemala had forced the ouster of some senior spies.

But Tenet built up the CIA's clandestine service, sharpened its scientific capabilities, changed its schools and training programs, paid some of its Cold War veterans to retire, and sent hundreds of new operatives overseas without the benefit of traditional diplomatic cover. "People are no longer operating just out of embassies, but out of all the back alleys in the world where we need to operate," said former CIA general counsel Jeffrey H. Smith.

The agency's budget expanded slowly in the late 1990s, to reach about $3 billion before the 2001 attacks, but Tenet was able to secure at least $1.5 billion more in the aftermath, in an implicit endorsement of the new path on which he immediately set the agency. The entire national foreign intelligence budget, which Tenet divulged in 1998 was $26.7 billion, has evidently grown to about $40 billion since then, said Steven Aftergood, an analyst at the Federation of American Scientists.

But the first managerial accomplishment many of Tenet's colleagues mention is that he brought a human touch to the director's office, where his more effete predecessors included a professor of chemistry at the Massachusetts Institute of Technology, a prominent corporate lawyer, a career CIA official and a federal judge -- four men who rotated through the job in a total of six years.

The son of a Greek restaurant owner from Queens, Tenet instead prowled the halls of the CIA with an unlighted cigar in his mouth, slapping backs and extending impromptu invitations for chats in his office. He jogged on the CIA grounds and ate in the cafeteria, behaving like a gregarious politician by meeting with former CIA officials and taking pains to woo the leadership of the agency's historically independent clandestine service.

"The most important thing he did was restore morale and bring in a whole new generation of officers" whose skills more closely matched the agency's new priorities, Smith said. "He was universally admired" inside the building.

Well known for his bluntness, Tenet was unafraid to say "Hell if I know" to his staff if a problem seemed to defy solution, his colleagues said. But he was, at heart, a problem solver given to nervously smacking a carved Irish wooden club into his hand until a path through the thicket became clear.

With a relentlessly pragmatic style and a reputation for loyalty to his employers, Tenet has moved easily in Washington. He worked as a Republican Senate aide, then as a Democratic aide; he worked at President Bill Clinton's White House as a national security aide, then migrated to the CIA as deputy director.

Clinton appointed him director as his second choice, after Anthony Lake failed to win confirmation, and President Bush reappointed him on a recommendation from his father, over the opposition of congressional Republicans.

Tenet quickly established a close rapport with Bush, who officials say admired his broad sense of humor, plain-speaking style and reticence in expressing personal opinions. At Bush's request, Tenet has delivered the president's morning intelligence briefings in person for much of the past four years. "I am not a policymaker," he told the Sept. 11 commission. It is the administration's "job to figure out where I fit into their puzzle."

His priorities on taking the job were to focus on terrorism, proliferation of weapons of mass destruction and what he saw as a long-term threat from China. But by the accounts of several of his friends, Tenet's sense of priorities did not match those of the Bush administration. Despite the morning chats, they said, Bush has been closer to and more dependent on Vice President Cheney and Defense Secretary Donald H. Rumsfeld, who each expressed more alarm than the CIA about the security threat posed by Iraq.

According to the Sept. 11 commission, Tenet's deputy, John E. McLaughlin, became concerned by the summer of 2001 that top administration officials were unconvinced of the urgency of the threat posed by bin Laden. But Tenet was less worried, telling the commission later he thought the policy machinery was working in "a rather orderly fashion."

After the 2001 attacks, Tenet inserted CIA officers, carrying tens of millions of dollars, into Afghanistan to begin planning for the military campaign against the Taliban. Since then, the agency has played a key role in capturing two-thirds of bin Laden's original group, although bin Laden and his top aide, Ayman Zawahiri, have proved elusive.

Tenet has also told friends that the agency -- which in the aftermath of the terrorist attacks forged new partnerships with intelligence agencies around the globe and also works much more closely with the FBI -- deserves a share of the credit for the absence of any new terrorist attacks on U.S. soil.

Yesterday, Clair George, a onetime head of the clandestine service who was caught up in the Iran-contra scandal and received a pardon from President George H.W. Bush, recalled how questions were raised when the inexperienced Tenet took over the agency.

"He did a good job in a tough time," George said. But then he noted speculation about why Tenet -- who never really achieved the status of an insider within the Bush team -- had decided to quit now. "In the normal course of events in Washington," said George, who was around when Richard M. Helms was replaced as CIA director, "we normally push the weakest man off the lifeboats."

In March 1997, President Bill Clinton announced that he would nominate the acting CIA director, George J. Tenet, center, to head the agency. With Tenet are his wife, Stephanie, and son, John Michael.