Part of our current shock is our belated awareness of how easy it is for terrorists to move among us. They rented good homes, depended on us to train them in aviation and hand-to-hand combat, visited Las Vegas, counted their frequent-flier miles, threw parties for neighborhood children and twice attended events at our war colleges. One bin Laden associate, a bizarre double agent, served in the U.S. Army. At least two are American citizens. One naturalized American citizen, El Hage, was convicted in the bombing of the U.S. Embassy in Nairobi. Another American, Abdul Rahman Yasin, born to Iraqi parents in Bloomington, Ind., was indicted in the 1993 bombing of the World Trade Center and fled the country.

A few of the Sept. 11 bombers moved in and out of the country several times. Immigration checkpoints don't seem to be much of a barrier. If they are, nearly any terrorist can come here as a student without being tracked or ever asked to leave. In 1996, Congress set up a program to track the half-million foreign students who attend college in the United States. The American Council of Education has been fighting the plan because colleges want the money that foreign students pay. So far the program called for by Congress is still on the drawing board. Only 25 schools even bother to check to see whether people here on student visas are actually in school. The upshot is that if you get here on a student visa, you can stay as long as you want.

The media stress on bias crimes is important. Sikhs, who are neither Arabs nor Muslims, have been attacked simply for wearing turbans. As Mayor Giuliani said, cowardly attacks based on hate are exactly what we are supposed to be opposing now. Still, there is something unbalanced and one-sided about the anti-bias rhetoric. I have noticed no comparable stress on the heightened responsibilities of Muslim Americans.

The most obvious one is to help watch out for dangerous members of their communities. We need to know what groups Osama bin Laden has tapped into and what those groups are doing. The Muslim community can be of enormous help here. A retired CIA officer told The New Yorker magazine that he and other members of the intelligence community were particularly alarmed by the likelihood that the terrorists had been sheltered, and never betrayed, by Muslim communities in the United States.

We also need clarity from American Muslims on the role of American Islamic charities that have become focuses of concern because of alleged ties to terrorist groups. High on the list is the Holy Land Foundation of Richardson, Texas. Israel says Holy Land is a front for the wealthy terrorist group Hamas. One of Hamas' important recruiting tools is a promise of annuities to the widows and children of suicide bombers. The State Department concluded that Holy Land was in effect sponsoring terrorism by raising money for these annuities here. American Muslims should speak out about Holy Land. If it is a front, as it appears to be, call for it to be shut down.

Writing in The New York Times, columnist Thomas Friedman gently outlined another responsibility of Arab and Muslim Americans: to send positive word about America back to their homelands to combat the Great Satan image of the United States promoted by our enemies. So far, many speaking for the Muslim community have simply stuck to a distressing pattern: a few perfunctory words of regret for the terrorist attacks, followed by far more energetic denunciation of bias crimes. In the struggle ahead, the nation will expect more than this from our Muslim and Arab neighbors.