Washington ? The government plans to meet a year-end deadline for screening bags at airports by using many more machines that detect traces of explosives rather than the minivan-sized equipment initially expected to be the mainstay of efforts to keep bombs off airplanes.

Not only do the trace detection machines cost far less, but they are just as effective, Transportation Department officials said.

“We will insist on the same high standards for all airports, small and large,” Transportation Secretary Norman Y. Mineta told a U.S. Chamber of Commerce luncheon Wednesday in announcing how the department would meet the congressional deadline.

Sen. Kay Bailey Hutchison of Texas, the top Republican on the Senate aviation subcommittee, had some questions about the plan.

“I want to see exactly how it’s going to work,” Hutchison said. “It is an interim, and I would be adamantly against it if they were trying to substitute the trace detection for a real machine that is competent.”

And a spokesman for Rep. Jim Oberstar of Minnesota, the top Democrat on the House Transportation and Infrastructure Committee, said he wanted scientific proof that the trace detection equipment was as effective as the larger explosive detection machines.

“To use trace detection when it has not yet been proven to provide the same level of explosive detection would result in two levels of security,” said the spokesman, Jim Berard. “And it would provide terrorists with an open invitation to use the smaller airports where the weaker security is in place.”

House aviation subcommittee chairman John Mica, R-Fla., said there was no way to produce and install enough of the big, $1 million explosive detection machines by Dec. 31.

More than 2,000 of the machines would have been needed at 429 airports to meet the deadline. Mineta said the government will now need 1,100 machines, plus 4,700 trace detectors, which cost around $40,000 apiece. The latter work by having security agents swab luggage with handheld equipment, which is then analyzed for traces of explosives.

At some airports, Mineta said, all bags will be inspected with explosives detection equipment. Some airports will have only trace detectors and some will have a combination of the two.

The trade-off is that the trace detectors require far more trained security employees than the explosive detection machines, Mica said.

Even so, the new Transportation Security Administration plans to cap its work force at around 67,000 people, Transportation Department spokesman Leonardo Alcivar said.

That includes 32,000 passenger screeners to be trained by Lockheed Martin under a $105 million contract awarded Wednesday. Mineta, a former Lockheed Martin official, recused himself from the decision.