The Bush administration has decided to scale back and delay the debut of a vast airline passenger screening program until after the presidential election, federal officials said yesterday.

The decision comes after months of meetings with airline officials and lawmakers who pressed the administration to drop more controversial elements of the program, known as Computer Assisted Passenger Pre-Screening Program, or CAPPS II.

Big disagreements about the system remain within the Department of Homeland Security itself, with some officials viewing it as a major aviation security improvement and others fearing it could alienate voters who view CAPPS II as a surveillance system that pries too far into passengers' lives, sources close to the project said.

Officials have already used some elements of the program and it was scheduled to roll out in airports this fall. Department officials yesterday could not pinpoint a new start date or provide details on what aspects of the screening system would be dropped.

The program "remains, in my mind, one of the most important tools in the counterterrorism arsenal," said James M. Loy, deputy secretary of Homeland Security.

But, at least initially, the government would step back from plans to subject all passengers to CAPPS II screens, which marshal multiple government and private databases to assign each flier a risk level using a green, yellow or red color code, officials said. The extra screening may only kick in if a passenger is flagged as suspect under the current system, such as for paying cash for a ticket.

Officials said they also are likely to abandon plans to use the system to find passengers wanted for violent crimes.

Instead, sources familiar with the program said yesterday, the government will simply confirm a passenger's identity by, for example, asking to see a valid driver's license and then checking a commercial data service to check if it's authentic. Then an airline agent would match that name against increasingly robust watch lists of known terrorists.

While CAPPS II is on hold, the TSA plans this summer to push ahead with a more popular, voluntary program that allows frequent fliers to become "registered travelers" by providing personal information to the agency, along with a fingerprint or iris scan. If the agency accepts a passenger into the program, which requires a background check, the traveler will get an identification card that allows quicker passage through security lines.

CAPPS II was once described by the government's top security officials as the most important development in preventing terrorist attacks on commercial airliners. The government spent more than $60 million designing a computer system to verify a person's identity by comparing information from the airline reservation against commercial databases, such as those used by direct marketing firms.

Homeland Security Secretary Tom Ridge indicated that CAPPS II had been canceled in an interview published yesterday in USA Today. But some elements of the program are already being used to check foreign airline crews, some employees working at airports and some travelers who have volunteered in another security screening program, sources said. Officials also said they would continue with plans to test the computer network later this summer using passenger information.

Privacy advocates welcomed the announcement that the program would be smaller and some took credit for forcing the government to reconsider it.

"It was always a very questionable concept from a security concept," said David Sobel, general counsel for the Electronic Privacy Information Center, a privacy rights advocacy group in Washington. "The effectiveness was never demonstrated and we always thought it was likely to provide a false sense of security and divert resources."

But others involved in the issue said the program's delay continues to leave a vulnerable hole in the nation's aviation system.

"Aviation security is certainly far too important to play politics with it," said Sen. Ron Wyden (D-Ore.), who sits on the Senate Commerce, Science and Transportation Committee. "The American people have a right to know how the obvious need for air security will be addressed. I believe it can be done and still protect privacy."

CAPPS II was supposed to begin screening passengers this fall, but it faced opposition at nearly every step. U.S. and European airlines initially resisted participating out of concerns that it would require them to become part of national law enforcement to track wanted criminals, not just terrorists. Privacy advocacy groups also claimed the government wasn't providing enough information about how the system would work.

In February, the General Accounting Office concluded that the Transportation Security Administration had many steps to go before it could even begin testing the system.

The program was also hurt by news reports that revealed several agencies, including the TSA, had already received millions of reservation records from airlines to test early versions of the program without telling the public. The airlines admitted they had not informed their passengers about turning over the records, which included credit card information and personal telephone numbers and addresses.

Several airlines now face class-action lawsuits filed on behalf of passengers who said the carriers violated their own privacy policies.

Some American Airlines frequent travelers will be allowed to participate next month in the TSA's registered traveler program at Reagan National Airport. The program has signed up 2,000 passengers at airports in Minneapolis and Los Angeles.