For 38 years, the FBI waged a campaign of infiltration and harassment against a small Trotskyite organization called the Socialist Workers Party. The bureau staged burglaries, planted fake news stories and otherwise sought to discredited the party and its members, who, though pushing a radical political agenda, were engaging in peaceful and lawful political behavior. The 38 years, which ended in 1976, produced not a single arrest.

It is worth recalling this episode, along with the FBI's notorious Counterintelligence Program, or Cointelpro, which was used not to gather evidence of criminality but to suppress lawful dissent by anti-Vietnam War protesters and civil rights leaders in the 1960s and 1970s. For the national rage and horror over the deadly bombing of a federal building in Oklahoma City have, understandably, created a political groundswell for giving the FBI and other law enforcement agencies greater invasive powers to combat terrorism, domestic and international.

The calls for action come with little proof that these agencies need additional powers or that they could use them without running roughshod over the rights of law-abiding citizens. Indeed, even the FBI is uncertain it wants much added authority. Its highly respected director, Louis J. Freeh, is keenly sensitive about the bureau's tainted past and is known to want only relatively minor modifications in guidelines that have governed domestic security investigations since 1976.

Those guidelines, loosened under President Ronald Reagan in 1983, give the FBI substantial latitude to investigate potential terrorist plots. The FBI, the rules say, may initiate a probe "when facts or circumstances reasonably indicate that a federal crime has been, is being, or will be committed." But, to deter abuses, they state that all investigations "shall be based on a reasonable factual predicate and shall have a valid law enforcement purpose." This is a much lighter burden than the "probable cause" needed by police to question a criminal suspect. Reagan's attorney general, William French Smith, said in 1983 that the amended rules "should help to eliminate any perception that actual or imminent commission of a violent crime is a prerequisite to investigation." Once the basic "reasonable indication" threshold is crossed, the FBI is permitted to use informants, infiltrators, and--with court approval--wiretaps.