Chicago - ON Aug. 5, Prime Minister Tony Blair of Britain announced his intention to carry out a series of new antiterrorism measures, including deporting foreign nationals who justify the use of "violence to further a person's beliefs"; authorizing the denaturalization of British citizens who engage in "extremism"; and legislating a new "offense of condoning or glorifying terrorism."

After the July 7 bombings in London, it is understandable that the Mr. Blair would want to deal firmly with those who incite violence. Although the loss of life and property caused by the Sept. 11 attacks far exceeded that in London, the United States was at least spared the constitutional dilemma of having to deal with a situation in which people in the United States encouraged American citizens to take part in the violence. But suppose that had been the case on Sept. 11, or suppose such a situation were to arise in the future. Would we respond any differently than the British?

The United States has a long and unfortunate history of overreacting to the fears and anxieties of wartime and excessively restricting the freedom of speech. This was so, for example, in 1798, when the United States was on the verge of war with France, and during the First World War. In both instances, the United States made it unlawful for any person to criticize the president, Congress or the government. Of course, Mr. Blair is not calling for such a far-reaching ban on seditious utterance. Rather, he is targeting only speech that glorifies or justifies acts of terrorism. On its face, this seems sensible.

But as Supreme Court Justice Felix Frankfurter noted in 1951, speech that extols political violence is often "coupled" with sharp "criticism of defects in our society." For that reason, Justice Frankfurter said, there is an important public interest "in granting freedom to speak their minds" even to those who advocate the use of force to bring about political change. A democratic society must protect itself against violent attack, but it cannot do so by preventing its citizens from hearing even sinister criticism that defends the use of violence.