Starting this week, all airlines, foreign and domestic, flying to the United States will be required to provide the U.S. Customs Service with detailed information about everyone on board or risk having their passengers face major delays when they arrive at American airports. It's part of the Aviation and Transportation Security Act that President Bush signed into law this month - a measure designed to enhance airline security in the wake of September's terrorist attacks. But not all airlines are ready to comply.

This new law will allow the government to know much more about the millions of passengers traveling to the United States, including their complete itineraries while in this country. In light of September 11, the Customs Service is ordering airlines to e-mail a list of everyone aboard planes destined for an American airport -- including passport, visa information and itineraries before touching down on American soil. Arriving passengers will then be checked against data bases to identify potential terrorists.

Many airlines - including American carriers - already provide this information voluntarily through what is known as the Advance Passenger Information System, or APIS.

"There are currently about 58 international air carriers that do not," says Kevin Bell, U.S. Customs Service spokesman. Among them is Saudi Arabian Airlines - the flagship carrier of the country that was home to 15 of the hijackers involved in the September 11 terror attacks. "The 58 airlines that are currently not participating, that is a national security concern to the United States," he says. "So, basically, if you're one of the 58 international air carriers who currently do not transmit APIS data, we will step up inspections of your flights and that will probably cause some delays."

Another is the Russian carrier Aeroflot, which wants to comply but says it does not have the required equipment. The airline plans to ask the United States to provide it.

Ron Lovas of the Airline Pilots Association thinks the flying public won't object to stepped up screening of arriving passengers. "I have to believe that, given the world after the 11th of September, that unless you're one of the terrorists, I suppose, you're going to want to submit to this because it makes for a safer world and it certainly makes for a more secure flight.," says Mr. Lovas.

Still, it's not clear whether such a measure would have prevented the September 11 terrorists from entering the country, since some of them had entered and left several times before the hijackings. These new measures take effect Thursday.