he terrorist attacks yesterday were intricately planned and carried out with precision. But what made them so devastating, physically and psychologically, was the way terrorists willing to sacrifice their lives swiftly turned unarmed civilian airplanes into guided missiles and left America with no obvious response.

The new kamikazes of the 21st century bore no flags or markings. They hid behind ordinary citizens, and their targets included ordinary Americans. By hijacking civilian airliners and riding them into the World Trade Center and the Pentagon, they used the very accessibility of an open society to wound that society.

Nobody doubts America's clear military superiority. But the lesson of yesterday seemed to be that even such power is vulnerable and may offer no redress against terror.

Because this was not a straightforward military attack, there is no simple military response. Certainly, shooting down all wayward civilian airplanes is not the answer.

The response will require better intelligence, especially human intelligence about terrorist cells, heightened security precautions and perhaps more forceful and riskier military action to pre-empt and to retaliate. Even then, as the far more experienced Israelis have learned, Americans will remain somewhat vulnerable to suicidal terrorists.

The obvious vulnerability of the buildings heightened the sense of shock. It is relatively easy to defend a military base or fortified bunker. But it is virtually impossible to insulate all of the United States government buildings and commercial centers against a suicide attacker.

In the long run, the United States will face the challenge of finding an enemy that has preferred to be largely anonymous and guarding against attacks without hobbling its own way of life.

During the Second World War, the Japanese pioneered the use of kamikaze planes. The kamikazes sank 34 ships and damaged hundreds or others. During the battle off Okinawa, they killed almost 5,000 men.

But yesterday's attacks, on a society at peace in a time of peace, carried out by attackers who took over civilian aircraft, appeared more sinister.

In recent years, there has been much discussion at the Pentagon about missile attack with chemical, biological or nuclear payloads. The success of yesterday's attacks does not mean that Washington should not also prepare for future dangers.

One striking thing about yesterday's attacks was the use of the crudest of weapons: unarmed civilian airplanes.

But taking control of them required meticulous planning. In a carefully coordinated operation, the attackers exploited the weaknesses in America's security.

They took over civilian airliners on domestic flights, which have less security than those on international routes. The flights originated from different cities and involved different airplanes. So this was not a simple inside job. Indeed, it is likely that the terrorists had the skills to fly the aircraft, at least for the final seconds that were needed to put them on their suicide courses.

In another reflection of careful planning, the structures hit, while symbols of the United States might, were soft targets. The Pentagon, a vast and essentially undefended office building, sits astride a major airline route. It has barriers to stop truck bomb attacks, and metal protectors and bomb detection machines at its entrances. Like the World Trade Center in New York, it had no protection from the air.

In the short run, the terrorists accomplished their objectives. The business of government virtually ground to a halt, and the air traffic system was paralyzed. From Asia to the Balkans, there was one main news event: the attack on the sole remaining superpower, one increasingly resented for its might even as its culture proves irresistible in most corners of the world.

Since the array of potential targets is so vast and since the terrorists are seemingly willing to accept any risk, it is vital to have human intelligence about a terrorist cell's plots. Yet obtaining "humint," as the Central Intelligence Agency likes to call it, has been dismayingly difficult.

The American intelligence establishment excels in technical collection, satellite photos and communications intercepts, but not in the strategic placement of infiltrators and spies. This has given the terrorists the element of surprise.

Another way to prevent attacks is to stop the terrorists ahead of time. The attacks yesterday are likely to lead the United States to accept a lower burden of proof about culprits and to take more risks in exacting retaliation.

The cruise missiles fired into Afghanistan at Osama bin Laden's men after the bombing of American embassies in Kenya and Tanzania in 1998 were weapons chosen to avoid the risk of American casualties, not ensure the destruction of terrorists.

Taking the fight to the terrorists could mean overcoming the abhorrence in the Pentagon of putting troops on the ground; it may well mean dispensing with the illusion that long-range, high-tech weapons are the answer to all of the Pentagon's problems.

There has been nothing in Defense Secretary Donald H. Rumsfeld's defense planning reviews so far that suggests the United States military will be better able — or more willing — to tackle such missions.

Still, if finding and targeting terrorists was easy, Mr. bin Laden, the suspected mastermind behind the bombings in Kenya and Tanzania, as well as a leading suspect in yesterday's attacks, would have been killed or arrested by now.

Defensive measures are also part of the answer. Undoubtedly, security at American airports and office buildings could be improved. Domestic air travel has not, up to now, involved the same stringent security as international flights.

In Moscow, civilian aircraft are not allowed over the capital. Airports are on approach routes to the city. That did not stop a young German adventurer from landing a plane in Red Square in 1987. But it does make commercial overflights the exception, not the rule. Is official Washington prepared to shut down its most convenient and recently modernized Ronald Reagan airport?

Gen. Henry H. Shelton, the chairman of the Joint Chiefs of Staff, said that the American military stands ready. The question is for what.

Washington's enemies, and its allies, will not only be waiting to see if the United States has the will to strike back. They will be also be waiting to see if it has the military ability to do so successfully. A strike at a mistaken target or an errant missile will not be much of a deterrent.

Nor will one raid, even a successful one, be a magic answer. People ready to fly an aircraft into a building are not likely to give up if American warplanes fly after them.

The terrorists are in the fight for the long haul. If the Pentagon is serious about fighting back and blunting the terrorist threat, it needs to be, too.