WASHINGTON -- Almost from its founding in 1948, the CIA has used American, and occasionally foreign, corporations to provide "non-official cover" for its activities abroad.

In the 1960s, the agency used patriotic appeals to recruit legitimate firms for cover purposes. A major Illinois corporation that did extensive business abroad had CIA officers hidden among its overseas staff. A large Chicago law firm allowed CIA officers who were trained as lawyers to "join" its overseas offices.

Some CIA officers posed as journalists, though usually as part-time, non-staff reporters for major news organizations. A 1977 investigation by The New York Times found that news organizations providing U.S. intelligence officers with journalistic cover included American broadcast networks and news magazines, as well as several major U.S. newspapers. The CIA says it subsequently disclaimed future use of full-time journalists employed by major American news organizations, including stringers and foreign reporters. .

Cover positions with legitimate corporations are the most difficult for the opposition to penetrate. Knowledge of the arrangement is usually limited to the company's top two or three people, who pay the CIA officer's salary from their corporate accounts after being reimbursed by the federal government.

"All your taxes are reconciled with a covert tax system within the IRS," said a veteran CIA officer. "Even if you got into IRS records, there would be no indication you were a NOC," CIA shorthand for an officer operating under "non-official cover."

In the popular imagination, the NOC has been defined by "The Spy Who Came in From the Cold" and "The Ipcress File." In fact, the job is arduous and thankless, and rarely glamorous.

One NOC, who posed for several years as the editor of an English-language newspaper in a European capital, spent most of his time putting out the paper, making sure to "plant" the odd news story or analysis written for local consumption by someone at CIA headquarters.

Companies began to shy away from such cover arrangements following the congressional investigations of the CIA in the mid-1970s, which left the CIA with no alternative but to set up its own dummy corporations. Corporate information available on the Internet makes such paper companies relatively easy to spot.

The basic details of these companies, like those of virtually any company doing business in the U.S., can be called up with the click of a mouse. The first tip-off is that there are not many details.

CIA front companies identified by the Tribune typically do not list any directors, officers or other employees--usually just a single CEO who, upon further investigation, appears to have no spouse or family, no mortgage history, no prior addresses, no driver's license or auto registration. In short, no existence.

There's little or no information about how much business the company does. Its physical address almost always turns out to be that of the lawyer who filed the incorporation papers, often in such out-of-the way venues as Oregon, Nevada and Montana.

The company's telephone number, if one is listed, rings at the switchboard at CIA headquarters in northern Virginia, where operators pretend to be an answering service that takes messages for the company's owner, who is perpetually "out of the office."

One Florida lawyer listed as the "registered agent" for a CIA dummy company, said he had never heard of the firm until he was contacted recently by the Tribune.

"I guess they just put me down for that one," the lawyer chuckled, acknowledging that he had a business relationship with the CIA that he otherwise declined to describe.

Several of the CIA's current paper companies were set up to act as the registered owners of its small fleet of aircraft, which range from giant C-130 cargo planes to eight-seat Gulfstream and Learjet executive jets that have been used to "render" terrorist suspects around the world.

The aircraft registered to those companies are a matter of public record, accessible through the Web site of the Federal Aviation Administration, which makes available information about the type, ownership and other details of every civilian aircraft licensed in the U.S.

The FAA now also makes public, for free, its real-time data showing the position of every civilian airplane that is in the skies over the United States, or has departed for an overseas airport or is heading to the U.S. from abroad.

Those data are compiled and stored by a number of online services that, for subscription fees as low as $10 a month, make available an airplane's entire "flight history"--a cumulative record of the dates, times and places of a particular aircraft's takeoffs and landings over the past several years. Such information has aided European investigators and journalists in tracking the CIA's abductions of suspected terrorists living abroad.

Some aviation Web sites even send subscribers an e-mail message whenever a designated aircraft files a flight plan showing its position, its destination and its intended take-off and landing times, making it possible for journalists and other interested parties to track the movements of the CIA's air fleet via their cell phones.