"The story begins," Laura Whitehorn wrote, "in May 1985," when she was arrested by FBI agents looking for "fugitive revolutionaries" {Outlook, Feb. 25}. This, though she was not a fugitive, and no charges were pending against her.

Not quite. The story actually began much earlier, when, according to a Senate subcommittee, Whitehorn joined the Weatherman faction of Students for a Democratic Society. It eventually became the Weather Underground Organization, which the FBI said was responsible for at least 40 bombings from 1969 to 1975.

In 1975, the Senate subcommittee, which called WUO "a revolutionary organization dedicated to the violent overthrow of established power in the United States," listed Whitehorn as a member of that organization and noted her arrests for disorderly conduct, conspiracy, malicious mischief, malicious prowling and conspiracy to commit unlawful acts. The report also noted that she was possibly part of Weatherman's above-ground support.

The FBI has identified Whitehorn as affiliated with the May 19 Communist Organization, which it has linked to the October 1981 Brinks robbery-murders in Nanuet, N.Y. Of the score or so people indicted in connection with the robbery, one-third have been associated with the M19CO, according to FBI reports. That robbery left one Brinks guard and two policemen shot to death and two others wounded. Other members of the M19CO have been convicted of a range of terrorist offenses, according to the FBI and press accounts, which helps explain why FBI agents confronted Whitehorn at a Baltimore apartment on May 11, 1985.

Two others identified by the FBI as members of M19CO -- Marilyn Jean Buck and Linda Sue Evans -- had been arrested in Dobbs Ferry, N.Y., earlier that same day. Buck carried a loaded revolver, Evans a loaded automatic pistol. Buck -- reportedly the only white member of the Black Liberation Army -- was wanted at the time for a number of offenses. The FBI said that both had been observed at Whitehorn's apartment the day before.

Armed with an arrest warrant for Alan Berkman, who was wanted in connection with the Brinks robbery, Bureau agents knocked on Whitehorn's door, identified themselves and asked to enter. She refused to let them in. Hearing what they believed to be the shredding of paper evidence, they broke in. In a series of searches of the the apartment the FBI said it found: weapons, including an Uzi semiautomatic 9mm, a .38-caliber revolver and a .22 automatic pistol with a silencer; bombing components; $10,000 in cash; hundreds of pieces of false identification as well as equipment to produce false identifications; stolen driver's licenses; police department patches; two badges from the N.Y.C. Police Department; wigs and theatrical makeup kits; one U.S. Air Force and partial Army uniform; surveillance logs indicating a "casing" of banks and corporate and government locations; a police scanner; CB radio equipment; intelligence files on police and the FBI; bulletproof vests; terrorist instruction manuals; a copy of the FBI's "1983 Summary of Terrorist Incidents"; and a copy of the attorney general's "Guidelines on the Conduct of Domestic Security/Terrorism Investigations." Also in a folder marked "In Progress," were diagrams and photographs of several potential bombing targets, including the Old Executive Office Building and the U.S. Naval Academy.

The FBI's search of Whitehorn's apartment found evidence of its use by ultra-radical groups suspected of 16 bombings since 1982 -- including that of the U.S. Capitol in November of 1983 -- and a list of 14 other potential bombing targets, according to FBI testimony before a Senate subcommittee.

Two more reputed M19CO members -- Berkman and Elizabeth Ann Duke -- were arrested in Doylestown, Pa., also in May of 1985. Both were armed with handguns and had an extensive store of dynamite and other terrorist items at the time of their arrest. The FBI estimates that it was able to prevent 14 terrorist incidents in 1985 as a result of the Berkman-Buck-Whitehorn arrests and the search of Whitehorn's apartment.

As Whitehorn noted, she was indicted in May of 1988 on conspiracy bombing charges. The outcome of that prosecution remains uncertain; meanwhile, she is being held in preventive detention pending trial.

The "most basic function" of government, the Supreme Court has said, is "to provide for the security of the individual and of his property." Contrary to her claims, the case of Laura Whitehorn is a compeling argument for the constitutionality and the practicality of preventive detention. -- Francis J. McNamara

The writer is a former executive secretary of the Subversive Activities Control Board and a former staff director of the House Committee on Un-American Activities.