Top federal officials, increasingly concerned that terrorists will attack U.S. commercial aircraft with shoulder-fired missiles, are developing plans to thwart such strikes with measures that range from sophisticated anti-missile technology to simple changes in takeoff schedules.

An interagency task force that reports to the National Security Council is also coordinating emergency inspections of every large U.S. airport to determine their vulnerability to the small, portable missiles, senior government officials said. And the task force is planning a public education campaign designed to teach police departments and citizens who live and work near airports to identify the missiles if they see them being assembled.

While acknowledging their alarm at the danger posed by portable missiles that may be fired at the approximately 6,700 commercial aircraft operating in the United States, administration officials stressed yesterday that the highest echelons of the U.S. government are focused on the threat and are determined to maximize the traveling public's safety.

"We have drawn together the best thinkers in government and in the contracting world" to address the issue in recent months, said one senior government official. "We now grasp the threat, and we grasp our options."

U.S. air carriers, already staggered by financial losses caused in part by the Sept. 11, 2001, terrorist attacks, are arguing that the government should bear the cost of any required high-tech equipment, which could carry billion-dollar price tags.

"Protecting our citizens and defending our nation against threats of this type is the responsibility of our federal government," said Michael Wascom, a spokesman for the Air Transport Association, which represents U.S. carriers. "As with any aspect of providing for our national defense, this subject is best addressed by our government."

U.S. military and intelligence officials have been aware of the threat presented by shoulder-fired missiles for decades. And in the days after Sept. 11, 2001, they initiated high-level meetings on the possible danger. But two recent attacks against aircraft involving portable missiles added to the sense of urgency.

In May, a Russian-built SA-7 missile was fired at a U.S. military jet taking off from Prince Sultan Air Base in Saudi Arabia, but it missed its target. On Nov. 28, two missiles of the same brand and factory batch as the one used in Saudi Arabia were fired at an Israeli jetliner seconds after it took off from Mombasa, Kenya. They streaked wide of their target at almost the same moment an Israeli-owned hotel in Mombasa was destroyed by a car bomb that killed 16 people. Officials concluded that the al Qaeda terrorist network was behind all the attacks.

Guerrilla and terrorist movements have long used "man-portable" missiles to bring down passenger aircraft, killing hundreds of civilians. In the 1980s, Afghan fighters repeatedly brought down Soviet helicopters with U.S.-supplied Stinger missiles.

But the Mombasa attack may have involved the first such missiles ever launched against a passenger carrier far from a war zone, officials said.

The attack confirmed the belief of U.S. intelligence experts that al Qaeda has access to a supply of the weapons and may now be uncrating them as a new terrorist tactic. The interagency task force stepped up its meetings just days after the failed shoot-down of the Israeli jetliner.

The five-foot long missiles and launchers would be relatively easy to smuggle into the United States, especially since they can be broken down into component parts for easy transport, officials said. At 30 pounds each, they could be concealed in a van, arms specialists said. "Manpads" (or man-portable air defense systems) can be launched through the sunroof of a car or even through underbrush, giving the shooter a chance to flee, they said.

More than 700,000 of the missiles exist, though the number controlled by rebel militias, terrorists and criminal gangs is estimated in the hundreds or few thousands, arms experts said. Even so, the missiles are fairly easy to acquire -- underground arms dealers sell them for as little as $25,000 apiece from Peshawar to Beirut.

The interagency task force -- led by the Transportation Security Administration (TSA) and including representatives of the Pentagon, the FBI and the State Department -- held two days of meetings on the missiles in December. Last week, the group sent a preliminary report, weighing various government actions, to a top-level panel convened by the White House's NSC.

"The key finding is there is no single answer to this threat, no silver bullet," one ranking government official said. "We'll have to consider a number of things to reduce this threat, in a multilayered approach."

Already, U.S. officials have been dispatched in a stepped-up effort to persuade foreign militaries to destroy some of their missile stocks and to prevent the theft of the rest. Another step will be to educate the American public on how to identify the missiles if they see them, "while not wanting to scare anybody," said one official working on the issue. He cited as examples airport business groups and neighborhood watch programs in towns beneath flight paths.

Authorities said they may also vary the takeoff times of aircraft each day, a practice followed by Israeli commercial airliners.

Officials said the government will initiate a program to retrain commercial pilots in the technique of landing a jetliner once it has lost an engine. Each missile seeks out the heat that emanates from a plane's engine, but some aircraft with two or more engines have been landed after being hit by one of the missiles.

Senior officials said the solution ultimately lies in installing high-tech "countermeasures" on jetliners, and they are considering U.S., British and Israeli technologies in a classified program.

U.S. military aircraft for years have deployed decoy flares to befuddle heat-seeking missiles. Northrop Grumman Corp. is supplying U.S. Special Operations transport and gunship aircraft with a system that automatically detects a missile launch from the ground and directs an infrared beam at the missile, causing it to veer off course.

Two Israeli firms are marketing their systems to U.S. officials -- one, Israel Aircraft Industries, uses explosive pyrotechnics that fling hot flares from the aircraft to create a false target; the other, Rafael, sends out a hot, radiated beam of energy. Some experts expressed interest in the latter plan because carrying explosives on planes could be dangerous, and releasing flares could start fires on the ground. The missile itself could also cause damage to surrounding neighborhoods if an aircraft evaded it.

U.S. officials said they are particularly concerned that terrorists might acquire new, updated missiles, which have onboard sensors that distinguish between a hot jet engine and the heated decoys. The older models can only strike aircraft straight on from behind, and only on takeoff, but later versions can be fired from the side as a plane takes off or lands.

U.S. officials said it is impossible to estimate how much it would cost to develop and deploy such a system on thousands of U.S. airliners, but they noted that the price of each unit would drop as more were installed. Contracting experts said the cost could well be in the billions of dollars.

Airport officials are worried that any missile-defense initiative would cost huge sums of money.

"Airports will be very concerned that the federal government is hitting them with another unfunded mandate, for example to station armed guards around fence perimeters," said Michael Boyd, a Denver-based consultant to airports around the country. "Airport directors feel whatever they say to the TSA isn't going to register."

David Stempler, president of the Air Travelers Association, an activist group, said passengers would appreciate the heightened security offered by the missile protection measures, but that he fears adding high-tech systems to airliners would lead to canceled flights if the equipment malfunctions. He also expressed the concern that installing some of the new technologies could compromise safety.

"When it comes to changing things on an airplane," he said, "the motto is, above all, do no harm."

Staff writer Susan Schmidt contributed to this report.