WASHINGTON - When Umar Farouk Abdulmutallab casually boarded his flight for Detroit on Christmas Day, he unwittingly confirmed repeated warnings about the chronic, costly shortcomings of government efforts to create better systems to screen travelers for bombs, weapons, and other threats.

The incident in which Abdulmutallab allegedly tried to blow up a Northwest Airlines jet follows a long series of public and confidential government findings that the massive push for new high-technology systems - some of them promising almost science-fiction-like abilities to detect and communicate threats - often has fallen short. According to these findings, billions of dollars are being wasted on systems that do not work or are behind schedule.

In the months after the Sept. 11 attacks, federal officials pledged to use information technology to identify terrorists, while also creating new machines that would automatically detect explosives, sense whether passengers were lying, and scan other materials for threats.

The Homeland Security Department and intelligence agencies have spent billions of dollars to develop security systems, including more than $795 million to research and develop high-tech checkpoint screening equipment.

But government watch lists failed to identify Abdulmutallab as a likely terrorist, even though his name was put in one of the most important government databases after his father warned officials he could be a threat. And none of the high-tech equipment under development by the Homeland Security Science and Technology Directorate was used to screen him.

According to government reports, mismanagement of research, concerns about privacy, the high costs of installation, and, in some cases, opposition from industry and Congress have hindered the widespread deployment of 10 systems at airports in the United States and abroad.

Instead, in Amsterdam, Abdulmutallab merely walked through a standard screening machine that cannot detect the type of plastic explosive he allegedly carried in undergarments and tried to ignite aboard Northwest Flight 253.

Behind those shortcomings is another one, officials have found. A plan that would have helped focus the development of better screening technology and procedures - including a risk-based assessment of aviation threats - is almost two years overdue, according to a report this fall by the Government Accountability Office, the investigative arm of Congress.

The Transportation Security Administration "cannot ensure that it is targeting the highest priority security needs at checkpoints; measure the extent to which deployed technologies reduce the risk of terrorist attacks; or make needed adjustments to its [Passenger Screening Program] strategy," the GAO report said.

'Adaptable'

Homeland Security officials have acknowledged the setbacks but say they are committed to overcoming them. They said that mandates to minimize the impact of security on the aviation industry, the infrastructure challenges of installing equipment in airports, and the persistent concerns about privacy have all contributed to delays.

At the same time, officials said, meaningful improvements have been made in the last eight years, including a cohesive workforce of screeners, better baggage-detection equipment, and a relatively quick screening process.

Homeland Security spokeswoman Amy Kudwa said that since the Sept. 11 attacks, her department and the TSA "have made significant improvements to aviation security technology."

"We are driven by the ever-evolving threat environment to have adaptable, flexible technology that can address multiple threats," she said. "We are committed to working through the inherent challenges we face in deploying new technology that meets all of these needs, to ensure the safety and security of the traveling public."

One key system known as the Terrorist Identities Datamart Environment (TIDE), a classified network begun in 2004 that collects and distributes the names of people flagged for scrutiny, has been hindered in recent years by design limitations and problems with a $500 million contract for an upgrade.

Operated at the National Counterterrorism Center, the TIDE system was built quickly after Sept. 11 and lacked many features needed by the intelligence community, documents show. A contract to upgrade the system ran into serious trouble last year, in part because of poor planning and disputes among the contractors, impeding the ability of intelligence analysts to discover patterns and make connections among the growing pools of data they amass from around the world.

Repeated delays

Intelligence officials last year said the problems with the contracting project had been resolved.

Although Abdulmutallab's name was in TIDE, he was not tagged for further screening as a "selectee" on watch lists because, administration officials said, there was not sufficient information to warrant the higher scrutiny.

Details about his trip, which originated in Lagos, Nigeria, or the fact that he paid cash for his ticket, apparently were not in the system, intelligence officials said. Critics of the administration have faulted the government's failure to pick up on those warnings.

Another system designed for border screening, called US-VISIT, has been repeatedly delayed by technological and managerial hurdles. Homeland Security officials estimated that the project - to create a massive computer network to screen all U.S. visitors and match their identities against watch lists - would cost more than $7 billion. Government auditors estimated the project could actually cost tens of billions.

The push to use technology to improve aviation security was one of the most heralded initiatives after 9/11. But the development of the technology has sputtered.

In its report this fall, the GAO found that the TSA had been unable to deliver a "strategic plan" for security measures, including those at checkpoints. It came to the same conclusion five years ago.

At least 10 technology checkpoint projects have been in development by Homeland Security's science and technology office. Those projects include a "whole body imager" to look for hidden weapons or explosives, a shoe scanner, and an "explosives trace portal" that uses puffs of air to dislodge bits of explosive materials to be analyzed by sensors.

The Bush administration rushed the explosives machines into airports in 2006, even though TSA officials were aware that tests on earlier models suggested they did not perform reliably, the GAO found. The TSA halted the deployment later that year, and much of the equipment was later sent to warehouses.