Checked bags should be screened for explosives as they travel from the ticket counter to the airplane, the head of the Transportation Security Administration says.

John Magaw called for renovating airports to make room for the minivan-sized explosive detection machines in areas where bags now are sorted before being loaded onto planes.

"That's the goal of most airports," Magaw said Monday. "When you go up and check your bag, it goes on the conveyer belt and is then examined before it goes on the plane. It's the most economical and most logical way of doing it."

The inspections would be done without the passengers watching, though a traveler could be called if the machine's alarm goes off and the bag needs to be opened and searched by hand, officials said.

"The process of explosive detection screening then becomes invisible to the passenger," said Gina Marie Lindsay, managing director of Seattle-Tacoma International Airport, which handles 27 million passengers a year. "It does not add to the congestion of the check-in and passenger screening process. It just becomes part of the normal process of transferring the baggage from the ticket counter to the airplane."

The security agency faces a Dec. 31 deadline for screening all checked bags with explosive detection machines. Airport executives say they can't finish the renovations to house the equipment in time, and some have asked the Transportation Department to push Congress to relax the deadline.

Magaw, the undersecretary of transportation, reiterated Monday that the timetable would be followed. Until the renovations are done, he said, some airports would have explosive detection machines near check-in counters and others would use smaller equipment that finds traces of explosives.

Lindsay, one of 39 airport executives signing a letter asking to extend the deadline, said trying to meet the timetable would take time and money away from the efforts to renovate baggage areas for the explosive detection machines.

"We should be focused on getting that solution in place as fast as possible and not divert attention to meet a deadline by the end of the year," Lindsay said.

Not everyone supports Magaw's solution. The head of an advocacy group questioned the idea of checking baggage away from passengers.

"When the bags are checked out of the sight of passengers, the TSA might be exposed to claims that items were stolen, broken or lost in the process," said David Stempler, president of the Air Travelers Association.

Lindsay said passengers could be notified at the gate that their bags needed to be inspected and could be taken to an area to watch security employees go through their luggage.