For the third straight day on Capitol Hill, an official from the Homeland Security Department fended off questions about the development of a system to screen airline passengers that has raised privacy concerns.

Testifying before a Senate Appropriations subcommittee, Tom Blank, an assistant administrator at the Transportation Security Administration, said the program is under review for possible changes to reflect privacy and civil-liberties concerns, and he signaled that the program would not be ready until next year.

Blank said he could not give a timeline for implementing the Computer-Assisted Passenger Pre-screening System (CAPPS II) because it "depends on the outcome of the review." When directly asked by Sen. Patty Murray, D-Wash., about the interim steps to complete the review, he said those steps "go to layers of security."

He cited other programs in place or underway, arguing that the existing pre-screening program - which Sen. John McCain, R-Ariz., earlier this week noted did not identify the Sept. 11, 2001, terrorists - is not without value. Blank said the government has a "no-fly list" but added that it expects the Terrorist Screening Center (TSC) to help to provide pre-screening security until CAPPS II goes online. The TSC will be based on a unified watch list that officials have stated repeatedly will not be operational before year's end.

When asked what is delaying the process, Blank said the Bush administration is working to address the privacy concerns, a point supported by a top privacy advocate this week. "We have heard the concerns of the privacy and civil-liberties community," Blank said. CAPPS II "will not go forward until we satisfy those concerns."

Some observers have suggested that the delay is not due to technological issues but rather the political difficulty in forcing airlines to share their passengers' information with Homeland Security, especially months from a presidential election. Airlines have said they need a legal requirement to share the information, and Homeland Security officials this week were vague about the shape that requirement might take.

Officials also have insisted that the department has no data to test CAPPS II.

But on Wednesday, TSA chief David Stone revealed that five major airlines shared sensitive passenger data with private companies contracted by TSA to develop the CAPPS II technology.

The American Civil Liberties Union (ACLU) late Wednesday said the revelation raises "serious concerns" that the nation's privacy law was breached. ACLU also said the disclosure "should raise serious red flags" about privacy and due process related to the program.

The main focus of the hearing of the Transportation, Treasury and General Government Appropriations Subcommittee on was on racial profiling in airport screening.

At the hearing, Murray also noted the inclusion of a provision in the Homeland Security appropriations bill requiring the General Accounting Office to confirm that steps have been taken to protect personal privacy. She said a GAO report on the subject earlier this year found the department "woefully behind."