BAE Systems PLC and Northrop Grumman Corp. won $45 million contracts yesterday to develop prototypes of anti-missile technology that could protect commercial aircraft from shoulder-fired missiles.

Under the 18-month Department of Homeland Security contracts, the firms will test their systems on wide-body jets and obtain Federal Aviation Administration certification for the technology. The department has not decided whether the contracts will include live-fire testing, said Penrose C. Albright, the assistant Homeland Security secretary for plans, programs and budgets.

A team led by United Air Lines Inc. and including defense contractor Alliant Techsystems Inc. was eliminated from the competition.

Concerns about possible missile attacks on commercial airliners have mounted since terrorists narrowly missed shooting down an Israeli plane in Kenya in 2002. Shoulder-fired missiles also have been used to shoot down military and other aircraft in Iraq and Afghanistan.

The effort to defend airliners requires adapting military technology to commercial aircraft, an expensive proposition that has raised safety concerns. Industry experts estimate it could cost $7 billion to $10 billion to include the technology on the country's 6,800 commercial planes.

"We're very hopeful that this technology will come to fruition," Albright said. But, he added, "there are a lot of challenges here."

At the end of the contracts, the department will submit the results to Congress and the White House, which will decide whether to move forward, department officials said.

BAE, whose team includes American Airlines Inc., and Northrop Grumman both proposed laser-based systems that would confuse incoming missiles. BAE's proposal adapts a system used on some Army helicopters that detects incoming missiles, tracks them with lasers and emits enough energy to send the missile off course, company officials have said.

Los Angeles-based Northrop Grumman's technology jams the guidance systems of incoming missiles. The company's team includes FedEx Corp. and Northwest Airlines Corp. and will be tested on a Boeing 747 and MD-11.

"This program is an integral first step in a layered defense for our national airspace," David W. Zolet, Northrop Grumman's vice president of homeland security, said in a statement.

United's team proposed deploying flares similar to those used by military aircraft, including the C-5 and C-17, which emit small decoys to confuse heat-seeking missiles and send them off course. There were some questions about the technical readiness of United's flare-based proposal, especially given the aggressive timetable of the program, Albright said.

United said it was "clearly disappointed" not to be chosen, particularly because Homeland Security chose two contractors using the same technology.

"United made a point to be involved with this program from the beginning so we could make DHS aware of the issues facing commercial airlines. While we believe DHS has overlooked these issues, we will cooperate in any way we can as this program moves forward to ensure our required standards of safety, reliability, cost and performance are considered," the airline said in a statement.