ASHINGTON ó THE F.B.I. director Robert S. Mueller III says the bureau is reinventing itself to fight terrorists as its No. 1 priority, but what about the Central Intelligence Agency? The Sept. 11 attacks, though carried out on American soil, were hatched overseas, which is the C.I.A.'s turf.

The two agencies failed utterly to warn of the terrorist attacks on the World Trade Center and the Pentagon. With a joint committee of Congress about to investigate, the full white glare of publicity will be on the agencies and their directors, not only Mr. Mueller but George J. Tenet, the C.I.A. chief. Both men will have a lot of explaining to do.

Beyond the political uproar in Washington lies a deeper and even more troublesome question: Can the C.I.A. and the other spy agencies prevent another such disaster?

That, in turn, hinges on whether the C.I.A. can penetrate terrorist cells abroad and whether the F.B.I. can do so in this country without infringing on constitutional rights. This was brought into sharper focus last week when Attorney General John Ashcroft announced he had given the F.B.I. more authority to conduct domestic spying.

The C.I.A., to be sure, has taken steps to improve its own antiterrorism posture since Sept. 11. It has, for example, doubled the size of its counterterrorist center to more than 1,000 people; created a paramilitary unit to put its people into Afghanistan and perhaps other places, and encouraged friendly governments to detain some 2,300 people suspected of links to Al Qaeda.

But the agency's top spy, while recently pledging to "disrupt and defeat international terrorism," seemed to say in the next breath that the task was near impossible. In a little-noticed speech in April, James L. Pavitt, the C.I.A.'s deputy director for operations, insisted that the government "could not either prevent or precisely predict the devastating tragedy of the Sept. 11 attacks."

It was highly unusual for the man who runs covert activities to make a public appearance, and his words hewed to the line of other senior government officials, initially including Mr. Mueller ó until he reversed himself last week and conceded the bureau might have been able to head off the attacks.

The problem, Mr. Pavitt argued, was that "the terror cells that we're going up against are typically small and . . . all those personnel were carefully screened." He added "anything short of one of the . . . hijackers turning himself in to us" could not have prevented the slaughter.

Not everyone agrees with this dour view. Robert Baer, a C.I.A. case officer in the Middle East and Asia for more than two decades, was upbeat. "You can penetrate these groups," he said. "I recruited and ran an agent in Beirut who was a member of Hezbollah. They don't all have the same degree of belief. Some are opportunists and are vulnerable to recruitment for money, to protect their family or they're angry at something. Or for ideological reasons." C.I.A. officers trying to recruit agents frequently exploited these sorts of motives and vulnerabilities, and often met with success.

Mr. Bear added, "You've got to get to those people who have their doubts. I don't think we should look at terrorists as a monolithic group of brainwashed people. They do not all share the view that it is right to kill Americans or kill foreigners." But finding the person who might harbor such misgivings can be a tricky business at best.

Mr. Baer, whose recent book, "See No Evil," is critical of the C.I.A., also argued that the agency has depended too much on liaison arrangements with foreign intelligence services, in the hope they will pass on information from their sources. When a C.I.A. officer recruits an agent on his own, Mr. Baer said, it is a "unilateral" source.

"Getting unilateral, non-liaison sources, just isn't done any more," he lamented. "It's discouraged because it's risky. The risk runs from having a case officer killed to annoying another government. The old approach, where a case officer goes out and meets a source up in the mountains in Afghanistan, you are risking getting someone killed. No one is prepared to take that risk. They all go home at night and sleep in the embassy."

A major problem faced by both agencies is that Islamic radicals determined to inflict harm on America are not likely to volunteer their services to American intelligence. Even if one did, the obstacles are formidable. Milton A. Bearden, who ran the C.I.A.'s war against the Soviet forces in Afghanistan, said, "someone who looks Middle Eastern is going to have a hard time even getting through the barriers of a U.S. embassy. He will attract too much attention."

Mr. Bearden said that the agency faced a similar problem in Moscow, where the K.G.B. monitored the American embassy. Even the C.I.A. officers had diplomatic license plates that identified them as Americans, but this led to a solution. "In Moscow everybody kept their car windows open a crack," said Mr. Bearden, "enough to drop in a note." This worked, if rarely.

"People are critical that we hung out in embassies, but that was our flytrap," Mr. Bearden said. "We made sure we were known to the K.G.B. resident in any given capital. So that the resident and key guys would know who to come to if they wanted to." Within the C.I.A.'s directorate of operations, its covert arm, the practice was known as "hanging out the shingle."

At first glance it might seem that the C.I.A. and the F.B.I. could apply some techniques that worked in the cold war to fighting the newer battle against terrorists. The C.I.A. counterintelligence officer Aldrich H. Ames, arrested as a Soviet spy in 1994, betrayed dozens of agents, 10 of whom were executed. Though a disaster for the C.I.A., it revealed that the agency had been able to develop an extensive network in Russia.

Could the intelligence agencies be similarly successful in recruiting Islamic fundamentalists? Mr. Bearden was cautious. "In the 50 years of cold war," he said, "we primarily dealt with people who'd made up their minds and decided to volunteer, including almost everyone Ames killed. For the most part, almost all were walk-ins."

Not all C.I.A. officers work under embassy cover. Some are "nocs" (pronounced knocks) who operate under nonofficial cover, perhaps posing as an oil company executive in the Middle East. "Even if you are a nonofficial cover guy," Mr. Bearden said, "it's not likely you can sit down in a cave with a cup of tea and convince a terrorist that the American way is the way to go."

Against such harsh realities, there are basic steps the C.I.A. could take, from hiring more Arabic linguists to offering competitive salaries to improving relations with the F.B.I. Suspicion and friction still impede cooperation between the two agencies.

ONE old hand said the C.I.A. will have to rely more on other governments. "We are going to have to have much more robust operations with Jordanians, Egyptians, maybe even Libyans. We have to convince leaders of these countries this is in their interest."

Another retired C.I.A. officer, who asked not to be identified, took issue with Mr. Pavitt: "I've seen foreign services recruit fundamentalists with honey traps, film them with a woman. It's amazing what you can do, even with ideological sources. Suppose you had pinpointed the group in Hamburg. You could have used entrapment. Or offered them money to do some innocuous study. Once they start signing receipts you say, `I really work for C.I.A. If you don't cooperate we'll say you are a C.I.A. agent.' Sure, most won't cooperate ó but some will.

"The Arab services, the Egyptians and Jordanians, have recruited people. The Jordanians put pressure on families. In Jordan they cut off water and electricity of the family of one terrorist, and gave a cell phone to the mother who called the kid and said `I have to talk to you.' The kid came home and worked for the Jordanian service.

"We have penetrated these groups. But the only way to do it is to use unsavory methods, blackmail. You have to put people on the ground. You can't do it 9 to 5. "