XFORD, England -- Viewed from England, what happened last Tuesday looked not like Pearl Harbor II, but like the London Blitz. That was one of many reasons for the outpouring of sympathy for America after the attacks on New York and Washington.

Without suicide bombers and without high-rise targets, this kind of death and devastation took the Luftwaffe weeks to achieve in 1940-41. During those dark days, it was Edward R. Murrow, CBS's bureau chief in London, who brought home to American radio listeners what London was enduring. Last week Britain felt the flames in New York, thanks to the still more vivid transmissions of satellite television.

Yet as the smoke clears, both literally and metaphorically, the mood in Europe is one of growing disquiet as well as sincere sympathy. A week ago it was impossible not to offer unconditional support to an America in agony. Today, however, there is a growing apprehension about what America's allies may have committed themselves to when they invoked, for the first time, Article 5 of the North Atlantic Treaty, with its affirmation that "an armed attack against one or more of them in Europe or North America shall be considered an attack against them all."

To be sure, Britain's prime minister, Tony Blair, has dutifully toed the American line: "Whatever the technical or legal issues about a declaration of war," he said Monday, "the fact is we are at war with terrorism." The British public seems ready for a fight: an opinion poll this week suggested that as many as two-thirds of the people here want military action.

And there is support for such action on the continent as well. Spain is solidly behind the United States and has already offered the use of its air bases. The European Union foreign policy chief, Javier Solana, called this week for a "grand international coalition to fight against this plague of terrorism."

Yet it would be a grave mistake for President Bush and his advisers to take such words to mean unconditional support for whatever retaliatory measures they decide on.

To some extent, the anxiety comes from those in the usual anti-American quarters, who regard any blow to the United States ・no matter how terrible ・as just retribution for past misdeeds. There is also the familiar European hankering after an independent foreign policy, unconstrained by American military objectives. American talk of "war" clearly makes many European leaders squirm. The Norwegian government was conspicuously quick to say that despite the NATO declaration, it did not regard itself as at war. Likewise, Defense Minister Antonio Martino of Italy said, "The term 'war' is inappropriate."

Even the big European players are becoming more circumspect in their remarks. In Washington Tuesday, President Jacques Chirac of France pointedly declined to use the word "war." Foreign Minister Joschka Fischer of Germany has warned against a "disproportionate response" by the United States, echoing remarks by the French defense minister, Alain Richard. All this was inevitable. We have heard it many times before, most recently during the Kosovo war and before that during the Persian Gulf war. Yet even among Europeans who are usually regarded as pro-American hawks, there is mounting unease. It is grounded in the fear that the United States does not know what it is getting into. This is not a war like World War II. It is a continuation of a war against terrorism that Europeans have been waging for more than 30 years. In this war, Americans are novices.

Since 1968, there have been 500 hijackings around the world and more than 4,000 recorded terrorist bombings. Although Americans abroad were often the targets, virtually none of these attacks occurred within the United States. In Europe, it was different.

The Irish Republican Army has never come close to killing so many people at a stroke as happened in the World Trade Center attack; nor has the Basque separatist group E.T.A.; nor did the German Maoist Red Army Faction in its bloody heyday. But we in Europe have been living for decades with the daily possibility of lethal explosions, and we know that you cannot rely on stealth bombers to defeat the stealthy bombers on the ground.

Since February last year, for example, the so-called Real I.R.A. has been responsible for no fewer than seven bombings in London, of which the most serious, outside two Ealing pubs, happened little more than five weeks ago.

If making war on terrorists were simple, the forces of the I.R.A. and E.T.A. would have been smoked out and hunted down long ago. But terrorist organizations are not nation-states that can be vanquished in conventional war. To have defeated the I.R.A. in the 1970's, the British government would have had to adopt policies ・like the internment of all Republican suspects ・that could not easily have been reconciled with liberal ideas of justice. Nor should it be forgotten that the lion's share of the money that financed the I.R.A. campaign of violence came from the United States. Not even the most extreme Unionists were prepared to bomb Boston in retaliation.

The fear of indiscriminate retaliation by the United States is particularly acute in countries like France, Holland, Britain and Germany, which all have substantial Muslim populations. Only a tiny minority may respond to calls for a jihad, but that is reason enough for Europeans to feel nervous about American talk of a "crusade."

Europeans have another concern about American policy. To many, last week's attacks have made a mockery of the Bush administration's missile defense plans. How, they argue, can any form of Star Wars protect us when a gang of fanatics armed with nothing more than knives can kill thousands of people in minutes? The biggest menace we face today ・and all civilized societies face it together ・is not intercontinental ballistic missiles but terrorism, which requires a subtler means of defense.

In truth, this may not be a case of either/or. What is undeniable, however, is that some countries in Europe have been at war with terrorists for decades and they have learned some hard lessons in the process. The biggest lesson is that there are no quick victories. The foe does not line up his tanks for you to flatten, his ships for you to sink. His troops live among you. While it is possible to attack foreign bases of operation, a direct hit does not guarantee an end to future terrorism. The smartest weapon in this fight will be the spy who is capable of mingling among Arabs and Afghans undetected. Can America find such people today?

George W. Bush may well grow impatient with Europeans' urging him to be cautious. But their hesitations must not be dismissed as faintheartedness. Americans must steel themselves for a long, inglorious kind of war that governments in Europe already know only too well.