The government's proposal to allow small scissors and some other sharp objects back onto airliners is causing an uproar among flight attendants, families of victims of the Sept. 11 hijackings and several lawmakers.

Transportation Security Administration chief Kip Hawley on Friday outlined the proposal as part of a broader shift in airport security. The plan will allow airline passengers to carry scissors less than 4 inches long and wrenches and screwdrivers less than 7 inches long. The plan is scheduled to go into effect Dec. 22, just in time for the Christmas travel rush.

Hawley also revealed that there is intelligence suggesting that terrorists study the screening procedures at airports in order to evade them.

"We do have intelligence that terrorists do watch our screening process, it doesn't matter how much they survey because it will be unpredictable and they will not know what to expect at any time," he said.

Passengers should expect more randomness at security gates so would-be terrorists won't know for sure what they will see. For example, an airport might require all passengers to remove their shoes one day but not the next.

"It is paramount to the security of our aviation system that terrorists not be able to know with certainty what screening procedures they will encounter at airports around the nation," Hawley said. "By incorporating unpredictability into our procedures and eliminating low-threat items, we can better focus our efforts on stopping individuals who wish to do us harm."

Among the items no longer prohibited from airliner cabins: scissors 4 inches or less, and tools such as screwdrivers, wrenches and pliers that are smaller than 7 inches.

Reps. Ed Markey, D-Mass., and Joseph Crowley, D-N.Y., said Thursday they intend to introduce a bill called the "Leave All Blades Behind Act" to preserve the current prohibition on sharp scissors, tools and knives in airliner cabins.

"On Sept. 11, we witnessed the devastation and death that can be perpetrated onboard a plane with commonly-used items like boxcutters, and TSA wisely took action to ban such sharp objects. Now is not the time to overturn this ban, since we know that Al Qaeda continues to put passenger plans near the top of its terrorist target list," Markey said. "The Bush administration proposal is just asking the next Mohamed Atta to move from box cutters to scissors as the weapon that's used in the passenger cabin of planes."

Crowley noted that he lost his cousin, a former FDNY chief, on Sept. 11, "and the fact is that we are no safer today than we were 4 years ago."

"Flight attendants and airline passengers put themselves at risk everyday. There are more effective ways of increasing efficiency without compromising security," he added.

The TSA has said that small, sharp objects do not pose as much of as risk now that airplane cockpits have fortified doors.

Hawley has complained that airport screeners spend too much time confiscating small objects from innocent passengers. He wants them to focus instead on searching for what the TSA views as a more serious threat: improvised explosive devices.

While Hawley said Friday there is no intelligence suggesting IED attacks are imminent in the United States, there is significant concern this style of strike is not out of the question.

Airlines generally support the plan. So does the pilots' largest union, the Air Line Pilots Association.

Bob Hesselbein, the union's national security committee chairman, said pilots think it's more important to focus on passengers' intent rather than what they're carrying.

"A Swiss army knife in the briefcase of a frequent flyer we know very well is a tool," Hesselbein said. "A ballpoint pen in the hands of a terrorist is a weapon."

TSA screeners this year alone have confiscated 12.6 million prohibited items, including 3 million sharp objects, according to the Homeland Security Department.

They've also taken away 8.1 million lighters, the only item prohibited by law. Congress, concerned that terrorists would have an easier time igniting a bomb with a lighter than with matches, enacted the ban. It took effect April 14.

Rep. John Mica, R-Fla., chairman of the House Transportation Committee's aviation panel, agrees with Hawley that screeners should be looking for explosives rather than small, sharp objects that could be used as weapons.

"You have a huge army of pilots that are now armed, you have significant numbers of federal air marshals, you have secure cockpit doors, you have an alert public," Mica said. "Terrorists aren't dumb, they can see what the weakness in the system is."

More than 18,000 screeners have been trained on advanced explosives detection techniques, Mica said.

But Sen. Kay Bailey Hutchison, R-Texas, a member of the Senate Commerce Committee's aviation panel, objected to the policy shift. In a letter to Hawley, she wrote that the change "could undermine the progress we have made in securing our skies since the 9/11 attacks. Security demands vigilance; we cannot become complacent."

Markey said the TSA is presenting the public a false choice. If there aren't enough screeners to check for sharp objects and bombs, he said, then more screeners should be hired.

The Association of Flight Attendants supports Markey's initiative, as does The Southwest Airlines flight attendants' union, Transport Workers Local 556.

"Under no circumstance should potentially dangerous weapons be allowed onboard an aircraft," said Patricia Friend, Association of Flight Attendants-CWA International president.

"I have not spoken to a flight attendant at any airline that isn't outraged by this," added Thom McDaniel, the president of the Southwest Airlines flight attendants' union. "They want to focus more on explosives, but they're not even mentioning that the biggest threat to commercial aviation right now is still the fact that most cargo is not screened."

Justin Green is an attorney for the families of three flight attendants who died aboard American Airlines Flight 11, which Sept. 11 hijackers crashed into the World Trade Center in New York City. Two of the flight attendants, Bobbi Arestegui and Karen Martin, were stabbed by the terrorists. The third, Betty Ong, reported what was happening during the hijacking in a telephone call to authorities on the ground.

"The families are outraged that the TSA is planning on letting weapons back on board," Green said.

TSA spokeswoman Yolanda Clark said the agency has great respect for the families affected by the Sept. 11 attacks and for flight crews.

"Security in the aviation system requires all of us — TSA, airlines, airports and passengers — to work together," she said in an e-mail. "We will continue the dialogue."

One sign that the TSA is serious about turning more of its focus toward improvised bombs and explosives is the graduation of 12 new explosives detection canine teams that joined the TSA's National Explosives Detection Canine Team Program last month. The teams are assigned to transportation facilities in Atlanta, New York, Salt Lake City, Reno, Nev., Little Rock, Ark., and Tamuning, Guam. Canine teams are also in place in other airports around the country.

Canine handlers are instructed on explosives safety and safe handling and accountability of explosives canine training aids. During training, the dogs spend much of their time searching for explosives in specialized indoor and outdoor training areas that resemble the real transportation environment, including aircraft and terminals. The teams also practice searching warehouses, luggage and a parking lot filled with cars, trucks, vans and buses.

"This graduating class increases TSA's field resources, and provides greater flexibility in securing transportation resources across modes," said Dave Kontny, Director of TSA's National Explosives Detection Canine Team Program.

FOX News' Catherine Herridge and The Associated Press contributed to this report.