LOOK FOR BIG CHANGES IN U.S. TRAVEL.

For Americans traveling abroad, it has always been a jarring experience to land in the airport of a country where terrorism is a real and unrelenting threat.

For travelers accustomed to the open and comparatively genteel environment of the United States' domestic airports, it can be a disconcerting experience to encounter guards clad in combat fatigues and toting assault weapons, to be subjected to exhaustive questioning or bag searches, to walk alongside coils of razor wire or anti-car-bomb barriers outside the doors of a terminal.

Prepare to see these precautions and sensibilities take firm root in America in the coming weeks and months. In all likelihood, the innocence of a blithely mobile society was irrevocably lost Tuesday with the outbreak of terrorist war within our borders.

The changes are sure to represent a disturbing reality for many American travelers. Convenience is sure to be severely crimped. Liberties will be sacrificed. But a strong argument can be made that all will be for a worthy cause.

How to deal with it? With patience and understanding and a generous allowance of extra time for any trip, unless you're inclined to tie yourself into knots of anxiety and aggravation. If the U.S. comes to adopt procedures commonly in practice in other terrorism-plagued countries, this is what you can expect:

Extensive security checks:

It's not unusual when passing through an international airport to have special security teams with explosives-sniffing dogs working their way along lines of passengers waiting to pass through customs. My experience has been that these officers are not the least bit cursory about their work, and instead linger over each of your bags and make certain the dogs take as much time as needed to check each one.

Travelers at Israel's Ben Gurion Airport are urged to arrive at least three to four hours before departure. In addition to employing dogs and metal detectors and X-ray machines, El Al Airline security officials single out and interview every passenger before permitting the person to board.

You can minimize detention by removing particular items from your belongings when you pack for your trip: a pocketknife on your key chain, a can of pepper spray, a pair of scissors in your toiletries case.

One of the surest ways to send up a red flag in an airport of heightened security is to express annoyance if asked, for example, to empty the contents of a particular bag or submit to a search with a hand-held metal- detecting device. Patience is a virtue here. And try to remind yourself of this: If other passengers on your flight are being subjected to the same careful scrutiny, the relative safety of your flight will be heightened.

The prospect of profiling:

Upon arriving in London's Heathrow Airport a few years ago, I was singled out for questioning by two passport-check officials for perhaps 20 minutes, as passengers at other interview stations streamed past me. On another occasion, while crossing the Canadian border at a remote station, I was taken into a small room and interrogated for 45 minutes.

Why? Probably because I was a single man traveling alone, and in each case could not give exact details of places I planned to visit (both trips were intended to be free-form).

Any inconvenience seemed a small price to pay for security.

Another member of this newspaper staff who recently visited Jerusalem observed an instance in which an Arab couple were questioned for more than an hour, and their belongings subjected to multiple searches by different security teams and also screened by special, high-powered X-ray equipment.

The unknown passenger:

Don't be surprised if in the near future an armed federal marshal will be assigned to every flight, domestic or international, originating in this country. Such a precaution, routinely instituted by the Israelis, might have headed off all four disastrous plane crashes last week.

Such a security official would fly incognito, of course, and would be a sharpshooter trained in anti-terrorist techniques. Israel's El Al, which has such an individual on every flight, hasn't had a plane hijacked since 1968.

When traveling abroad, meanwhile, Americans should realize that they can be (and have been) potential targets of violence based entirely on their citizenship. There are ways to minimize risk, however.

One is to be mindful of your attire. Many Americans dress for a trip abroad as if they were headed to Disneyland: neon athletic shoes, cameras draped over their shoulders, the names of American products screaming out from their shirt fronts, their hats, their shoulder bags. Try to pick more neutral attire, and carry cameras in a small day pack or leather bag. On a recent trip to France, my wife blended in so well that she was asked for directions in French three times.

It's also wise to be mindful of the customs of dress for the country you're visiting. (This is especially true for women visiting Middle Eastern countries.) If in doubt, consult a nation's tourism bureau or a restaurateur in your community who hails from the country you intend to visit.

If you're sightseeing in another country - even a Western European nation - and you come upon a gathering that appears to be a political demonstration, immediately head in the opposite direction. Don't stumble up to it with your curiosity heightened and your camera snapping. If it's a rally in which anti-American fervor is being whipped up, you don't want to suddenly provide a convenient target for the wrath.

Finally - and particularly if you decide to visit one of the world's hot spots - consider hiring a local driver rather than exploring on your own in a car. A local driver will know what areas to avoid - perhaps a tourist site at which a political rally was convened that very morning. Also, he would be much better-equipped to talk your way out of a tense encounter.

Understandably, many Americans might be reluctant to travel anywhere beyond our borders for a while. Or even get on an airplane.

There is a still a wealth of tourism options here in the West that can be reached by car. And in time it might be healthy to ease pent-up anguish over last week's events by getting away for a couple of days. It's probably a good message to send to your children, too: You're not paralyzed with fear over the prospect of traveling anywhere.

Staff writer Richard Irwin contributed to this report.

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(1 -- 2) Heavily armed security officials, such as those at London's Heathrow Airport, left, are a common sight in international airports where terrorism has been a threat for some time. In the wake of terrorist onslaught, Americans should anticipate heavier security, including explosives-sniffing dogs, above, at their airports.

Steve Miller/Associated Press

Dave Caulkin/Associated Press