Concern is mounting that the US government is using antiterror laws - namely, the Patriot Act - to revive a now-discredited practice common during the cold war: the prevention of foreign intellectuals who are critical of administration policies from entering the country and sharing their views with Americans.

The practice, called ideological exclusion, became illegal in 1990. But a recent lawsuit - brought by the American Association of University Professors (AAUP), the American Civil Liberties Union (ACLU), and the PEN American Center under the Freedom of Information Act - is asking the Bush administration to explain its decisions to revoke or deny visas to several foreign scholars, and why they don't violate free-speech protections.

"This is about free speech, the purpose of colleges and universities," says Donna Euben, counsel for the AAUP in Washington. "We're not challenging the [USA Patriot Act] itself. We're just asking for information about its application to these particular scholars where there is no evidence that they have supported terrorism in any way."

In their suit, the groups cite the cases of several foreign scholars. One, Tariq Ramadan, is a prominent Swiss Muslim scholar who has condemned terrorism and routinely come to the United States on speaking tours in the past. In 2004, as he was preparing to take up a teaching post at the University of Notre Dame, his visa was revoked. The US government gave no formal reason, but press reports suggested the denial was based on "antiterrorism law." Another scholar, Dora Maria Tellez, is a former Nicaraguan government official who more than a decade ago was involved in the overthrow of the US-backed Somoza regime. She had been lined up to teach at Harvard University, but last January her visa was denied.

Administration officials aren't commenting on either case because the matter is now in the courts. But those who support the government's actions say it has a right and a duty to protect national security at a time of war. If it's concerned that a foreign national may promote ideas or activities that are antithetical to US interests, it has every right to deny that individual entry - and without an explanation.

The controversy is the latest illustration of the potential clash between commonly accepted civil rights and governmental efforts to protect national security. At the center of the debate about ideological exclusions is a little known provision of the Patriot Act, called Section 411. It allows the government to refuse admission to foreign nationals who, in the government's view, "have used [their] position of prominence within any country to endorse or espouse terrorist activity, or to persuade others to support terrorist activity or a terrorist organization in a way the Secretary of State has determined undermines United States efforts to reduce or eliminate terrorism."

Administration critics have no problem with the idea of excluding terrorists or people who espouse it. But they're concerned the government has now so broadly defined "terrorism" that even people who have openly condemned it but are critical of US policies are now being denied entry.

"We have a right to know about how our government is using various immigration laws to censure ideas that Americans have a right to hear," says Melissa Goodman of the ACLU's legal department in New York.

The US has a long history of denying foreigners entrance if their political views are at odds with the government's. It goes all the way back to Colonial times and the Alien Sedition Act of 1798. It was revived in 1952 at the height of the cold war.

"It was believed that we had to stop the importation of communism into the United States, and it was especially so in the early and mid 1950s when [Sen. Joseph] McCarthy was at his zenith in terms of power," says Kevin Johnson, a professor of law at the University of California at Davis.

That law was revoked in 1990 because "it became increasingly clear that it was inconsistent for a country that is one of the great democracies of the world to exclude people from coming here because of their political beliefs," he says.

But supporters of ideological exclusion see it as an important governmental tool. "We have always had a policy that allows us to keep out aliens who are at ideological odds with the US," says James Edwards of the Hudson Institute, a nonpartisan think tank in Washington. He was opposed to the 1990 revocation and believes that critics' claim of a First Amendment issue is misguided.

"That's the same argument that's apparently being revived by the usual suspects on the left to deride the use of ideological exclusions," he says.

Critics of the government's use of the Patriot Act disagree. "We're concerned about these provisions of the Patriot Act because they give such more or less unlimited and unmonitored powers in certain respects to federal agencies to act essentially without any check on their exercise of discretion here," says Michael Roberts, president of the PEN American Center in New York. "That's what's disturbing here."