SOUTH HADLEY, Mass. -- It all seems so innocent. Atty. Gen. John Ashcroft wants to unleash the FBI to surf the Web for possible terrorists. And it could be, except for the insidious fact that each time politicians have "unleashed" an investigative agency, even for the best of reasons, bad things have happened without improving security.

In 1970, I wrote an article about the Army's surveillance of civil rights and anti-war movements. Its domestic-spying program employed 1,500 agents and was undertaken without authority from Congress, the president or even the secretary of the Army. My name was soon added to President Nixon's "enemies list" for a tax audit. The Army tried to monitor my incoming mail. Shortly before I was to testify before North Carolina Sen. Sam J. Ervin Jr.'s subcommittee on constitutional rights, Army colonels falsely informed committee staffers that I had fathered illegitimate children.

It was the stuff of intimidation--and it worked most of the time. Many former FBI agents said they would only provide information to the Senate subcommittee if their identities were not disclosed; few dared testify in public. In 1972, I was hired by Ervin's committee to analyze the information, stored on six computers, that the Army had obtained from its domestic political spying. The files showed that the Army had clearly violated the privacy and free-speech rights of hundreds of thousands of law-abiding Americans. But they also revealed how useless the spying had been--not one report pointed to any foreign or criminal involvement in domestic political protests.

Other domestic-spying programs have been similarly fruitless. In the 1950s and 1960s, the FBI, the Army, the CIA and many police department "red squads" clipped newspapers and attended public meetings with the aim of identifying people sympathetic to communists. Their agents also infiltrated many law-abiding groups in search of "reds" or fellow travelers. The Army, whose only domestic duty was to put down riots, eventually spied on every demonstration of 20 people or more. But all this snooping never predicted a riot or uncovered any plot, communist or otherwise, to turn a lawful protest into a criminal attack.

During the Cold War, the FBI undertook more than 500,000 counterintelligence investigations against domestic political groups. Not one produced an indictment. Yet the investigations gradually changed the character of the agency, from one chiefly concerned with law enforcement to one centered on spying.

Trouble was, the more the FBI thought of itself as an intelligence agency, the less it felt restrained by law. Without a statutory charter, Justice Department guidelines or meaningful legislative oversight, the bureau conducted thousands of burglaries, called "black bag" jobs, and opened hundreds of thousands of first-class letters. It also bugged, without warrants, people not suspected of any crimes.

Nixon's secret plan, hatched in late 1970, to use the FBI, Army and CIA to spy on critics of the Vietnam War ultimately contributed to his downfall, sent his attorney general to prison and persuaded the FBI to adopt the very guidelines that Ashcroft now finds "outdated" in the war against terrorism. But without those guidelines, harassment and dirty tricks are likely to be acceptable again as long as they are directed against suspected terrorists and their sympathizers and as long as the Bush administration can plausibly deny authorizing them.

Some say that would be OK if the spying helps protect us from terrorists. But the opposite is more likely to occur. The investigations Ashcroft envisions are almost certain to inundate analysts with so much irrelevant information that they won't be able to separate meaningful signals from the static.

Whether there was a significant intelligence failure leading up to Sept. 11 remains to be seen. If there was one, however, it probably resembled the failure that left Pearl Harbor unguarded Dec. 7, 1941: the inability to collate and analyze useful signals from many sources in time to prevent a surprise attack. One of the great benefits of the "outdated" FBI guidelines was that they protected the bureau from wasting limited resources vacuuming up domestic political trivia. Good intelligence work, like good sleuthing, requires a disciplined, focused, well-coordinated exploitation of promising leads.

The war against Al Qaeda will not be won at home. Mohamed Atta, the director of the Sept. 11 attacks, didn't reveal his plans in an Internet chat room. So, instead of unleashing FBI agents to spy on Middle Easterners in the United States, the government should hire hundreds of foreign-born linguists on a contract basis and send them off to track down leads in Pakistan, Indonesia or Kashmir. Other linguists should be hired to analyze the results, much as we used Japanese Americans to read Japanese code traffic during World War II. And most of these linguists should not be integrated into existing agencies. They should be assigned to new units free of the usual bureaucratic impediments to curiosity, imagination and initiative.

Would such measures prevent another terrorist attack in the United States? Probably not, but they will do more good and less harm than assigning English-only white guys to hang around New Jersey mosques or to monitor chat lines in Peoria.