WASHINGTON -- The war on terror is pressing the FBI and CIA, once two solitudes, to mesh in ways their operatives could not have imagined in scrappier days.
These agencies have skirmished over everything from political favor to cubbyhole office space. Their prime missions -- using investigation at the FBI to solve crimes, using spies at the CIA to prevent trouble -- have tripped over each other at times.
On a personal level, the tweedy intelligence officer and rumpled gumshoe may be overdrawn stereotypes, but ones that betray a different world view and way of doing things.
"It's been a rocky relationship," said Loch Johnson, an author on intelligence agencies who teaches political science at the University of Georgia. "These days it's very uneven."
The two agencies have been working systematically since the mid-1990s to combine their strengths and communicate more effectively than they did when the Potomac River between their headquarters stood as a mighty gulf.
Their long rivalry and recent collaborations will be one of the subjects for exploration in joint Senate and House intelligence hearings that begin this week, called to find out why the Sept. 11 attacks were not foreseen by either agency.
The effort to spur cooperation is most apparent at senior levels, where the CIA in Virginia and the FBI in Washington have placed top officers in the counterintelligence and counterterrorism operations of one another.
In the aftermath of Sept. 11, FBI Director Robert Mueller or a deputy has joined the daily CIA intelligence briefings given to President Bush, sitting in on the portion that deals with counterterrorism.
The CIA is sending 25 analysts to work with domestic FBI agents in an expansion of joint operations and officer swaps that have been taking place for several years.
"We have to do a better job of collaborating," Mueller said during a week in which he acknowledged widespread FBI shortcomings and set out steps to fix them. "I think both agencies have a lot to learn from working together in ways we have not worked in the past."
The unevenness Johnson referred to was evident before and after Sept. 11.
When Minnesota FBI agents took their concerns about alleged terrorist Zacarias Moussaoui directly to the CIA, they got their wrists slapped by superiors for going around their headquarters, FBI officer Coleen Rowley said in her whistleblowing memo to Mueller.
Moreover, the bureau did not tell the CIA about a pre-Sept. 11 memo from one of its Arizona agents warning of Arabs taking flying lessons. The CIA got it from the FBI this spring, after it was in newspapers.
John Deutch, CIA director in the mid-1990s, says some tensions between the agencies are natural. CIA success tends to be measured in foiled plots the public does not know about; the FBI's, in bad guys behind bars.
The fear, he said, is that an FBI tip to the CIA about an investigation might risk spoiling a prosecution. A CIA tip to the FBI could compromise a carefully nurtured source.
"Clearly the current structure is ill-suited to deal with catastrophic terrorism," Deutch said in a Foreign Policy magazine article written with former CIA general counsel Jeffrey H. Smith. They recommended giving the CIA chief more authority.
The relationship hit bottom some 30 years ago, Johnson said, when J. Edgar Hoover of the FBI and Richard Helms of the CIA stopped talking.
More recently, the Aldrich Ames case exposed a failure of communication that may have helped the CIA officer get away with selling secrets to Moscow until he was finally caught in 1994.
Despite longtime suspicions about Ames, the CIA did not tap FBI counterespionage expertise.
That case "proved that we could no longer tolerate petty bureaucratic jealousy and turf wars," said George Tenet, then a National Security Council official, now CIA director.
During the 1990s, the FBI's rapid expansion abroad raised tensions with the CIA as well as the State Department over how to coordinate their work and even split up office space.
All of that led to a 1996 meeting in Rome, drawing together foreign agents of the CIA and FBI in what participants called a loud airing of grievances and, at least for some, a catharsis.
"There are clearly cultural differences," says Robert S. Litt, deputy assistant attorney general at the time. But he says cross-agency coordination has improved.
Purging the old animosities will not be easy. When the agencies began swapping deputies, operatives called it a "hostage exchange program."
Mueller, referring to the CIA analysts detailed to work with the bureau, called them "detainees" instead of "detailees".
His jocular slip of the tongue indicated that even now, when everyone wants the national security apparatus to work seamlessly, a river runs through it.