The new rule for APIS, published in its final form Thursday, will require air carriers to transmit a final passenger list for all international flights to the Department of Homeland Security at least 30 minutes before the plane takes off -- instead of no more than 15 minutes afterward, as at present.

"Under the current rule, airlines provide what we call passenger manifest data ... after the flight has already left the ground," Chertoff told reporters at National Airport just outside of Washington Thursday. "That is too late."

The plan for Secure Flight is the latest effort by Homeland Security to roll out the new system, which has become a lightning rod for privacy and other concerns about the growing use of watch lists by the U.S. government.

Under the plan, the department will take over from the airlines the process of checking domestic passenger names against the so-called no-fly list, in reality a special sub-set of the U.S. Terrorist Screening Database. The use of the no-fly list has become fodder for late-night comedians following widely publicized incidents in which children, lawmakers and a senator's wife were erroneously identified as security risks and prevented from boarding planes.

Past efforts to implement Secure Flight have run up against congressional opposition, in part because of the department's insistence on comparing passenger names with information mined from commercial databases such as those held by credit agencies to try and weed out possible identity thieves and spot potential terrorists through suspicious patterns of behavior.

"I want to be very straightforward about this," Chertoff said. "Secure Flight will not do any harm to personal privacy. It's not going to rely on collecting commercial data; it's not going to assign a risk score to passengers; it's not going to try to predict behavior."

But officials acknowledge that precisely those kinds of efforts will still be made on international passengers, as APIS and other data, like that from the airlines' Passenger Name Records, will be crunched by the Automated Targeting System, a computer program run by the department's Customs and Border Protection directorate.

The Automated Targeting System "compares Passenger Name Records and APIS data with law enforcement records and threat-based scenarios," said the department's Privacy Officer Hugo Teufel III in a statement last week, "to intercept high-risk travelers, identify persons of concern, and identify patterns of suspicious activity."

And the system would retain that data for 15 years, Teufel said. Thursday, Chertoff said that the information from domestic passengers would not be retained. "We're not going to keep the (domestic) manifest data. We're simply going to take it, bang it up against the watch list, and then we have no more interest in it. ... (It will be) disposed of."

Chertoff said that by getting the department to do the screening rather than the airlines, Secure Flight would reduce the number of so-called false positives, in which an innocent traveler is misidentified as someone on the list.

"It will be a much more up-to-date watch list than the airlines have," he said, adding that under current arrangements the department supplied copies of the list to airlines, "and then the airline's ability to screen depends on how frequently they update their list. So if they're slow ... they're going to be more out of date."

But in reality, most of the problems experienced by travelers stem not from outdated information but from the presence on the list of certain common names. Sen. Ted Stevens, R-Alaska, for example, has publicly complained that his wife, Catherine, has been erroneously matched with the British pop singer and Muslim convert Cat Stevens -- watch-listed because of his support for Palestinian charities linked to groups considered terror organizations by the U.S. government.

Chertoff said the department would seek to reduce the number of these false positives by asking passengers to provide their date of birth and gender when they book airline travel.

"The whole point here is to help us get a little bit of information ... so we can differentiate the innocent passenger from the person with the same name who happens to be on a watch list. And if a passenger is willing to provide that information, the airline would send it to (us) and it's going to result in reduced inconvenience to the traveling public."

Airlines welcomed the changes. In a statement, Air Transport Association President and CEO James C. May said they applauded the new plans.

"If properly crafted, the programs will improve aviation security without adding to passenger privacy concerns. In particular, we look forward to a unitary data collection process that accommodates all government demands for passenger information and leads to the creation of a coordinated worldwide system."

May added, "In order to minimize unnecessary impact on the airlines, it is essential that the government carefully consider industry feedback on these programs."