"Academic colleagues, get used to it," warned the pro-Israel activist Martin Kramer in March 2004. "Yes, you are being watched. Those obscure articles in campus newspapers are now available on the Internet, and they will be harvested. Your syllabi, which you've also posted, will be scrutinized. Your Web sites will be visited late at night."

Kramer's warning inaugurated an attack on intellectual freedom in the U.S. that has grown more aggressive in recent months.

This attack, intended to shield Israel from criticism, not only threatens academic privileges on college campuses, it jeopardizes our capacity to evaluate our foreign policy. With a potentially catastrophic clash with Iran on the horizon and the Israeli-Palestinian conflict spiraling out of control, Americans urgently need to be able to think clearly about our commitments and intentions in the Middle East. And yet we are being prevented from doing so by a longstanding campaign of intimidation that has terminated careers, stymied debate and shut down dialogue.

Over the past few years, Israel's U.S. defenders have stepped up their campaign by establishing a network of institutions (such as Campus Watch, Stand With Us, the David Project, the Israel on Campus Coalition, and the disingenuously named Scholars for Peace in the Middle East) dedicated to the task of monitoring our campuses and bringing pressure to bear on those critical of Israeli policies. By orchestrating letter-writing and petitioning campaigns, falsely raising fears of anti-Semitism, mobilizing often grossly distorted media coverage and recruiting local and national politicians to their cause, they have severely disrupted academic processes, the free function of which once made American universities the envy of the world.

Outside interference by Israel's supporters has plunged one U.S. campus after another into crisis. They have introduced crudely political -- rather than strictly academic or scholarly -- criteria into hiring, promotion and other decisions at a number of universities, including Columbia, Yale, Wayne State, Barnard and DePaul, which recently denied tenure to the Jewish American scholar Norman Finkelstein following an especially ugly campaign spearheaded by Alan Dershowitz, one of Israel's most ardent American defenders.

Our campuses are being poisoned by an atmosphere of surveillance and harassment. However, the disruption of academic freedom has grave implications beyond campus walls.

When professors Stephen Walt and John Mearsheimer drafted an essay critical of the effect of Israel's lobbying organizations on U.S. foreign policy, they had to publish it in the London Review of Books because their original American publisher declined to take it on. With the original article expanded into a book that has now been released, their invitation to speak at the Chicago Council on Global Affairs was retracted because of outside pressure. "This one is so hot," they were told. So although Michael Oren, an officer in the Israeli army, was recently allowed to lecture the council about U.S. policy in the Middle East, two distinguished American academics were denied the same privilege.

When President Carter published "Palestine: Peace not Apartheid" last year, he was attacked for having dared to use the word "apartheid" to describe Israel's manifestly discriminatory policies in the West Bank.

As that case made especially clear, the point of most of these attacks is to personally discredit anyone who would criticize Israel -- and to taint them with the smear of "controversy" -- rather than to engage them in a genuine debate. None of Carter's critics provided a convincing refutation of his main argument based on facts and evidence. Presumably that's because, for all the venom directed against the former president, he was right. For example, Israel maintains two different road networks, and even two entirely different legal systems, in the West Bank, one for Jewish settlers and the other for indigenous Palestinians. Those basic facts were studiously ignored by those who denounced Carter and angrily accused him of a "blood libel" against the Jewish people.

That Israel's American supporters so often resort to angry outbursts rather than principled arguments -- and seem to find emotional blackmail more effective than genuine debate -- is ultimately a sign of their weakness rather than their strength. For all the damage it can do in the short term, in the long run such a position is untenable, too dependent on emotion and clich� rather than hard facts. The phenomenal success of Carter's book suggests that more and more Americans are learning to ignore the scare tactics that are the only tools available to Israel's supporters.

But we need to be able to have an open debate about our Middle East policy now -- before we needlessly shed more blood and further erode our reputation among people who used to regard us as the champions of freedom, and now worry that we have come to stand for its very opposite.