Vienna--This cultivated, blase, tourist-jammed city--whose streets are alive with the sound of music--is an excellent place to consider the third Islamic invasion of Europe.

The first invasion was stopped at Tours, in France, in 732 by Charles Martel. Islam fell back to Spain where it held on for 700 years and constructed a civilization far superior to any in Europe for most of those centuries. They discovered algebra and rediscovered Aristotle before the Catholic theologians of Europe.

The second invasion was halted here, in Vienna, in the 1683, in what, to quote the Duke of Wellington on another battle, was "a very near thing." After the fall of Constantinople in the mid 15th century, the Turks pushed north into the Balkans and routed the Serbs and the Hungarians. Twice they raced north to the Imperial Capital, the second time almost taking it. France and Spain, the Pope and the Prussians, the English and the Scandinavians were otherwise occupied. If Vienna fell, there was little chance that the Turks could have been stopped short of the English Channel.

The Polish army, however, commanded by King Jan Sobieski, arrived in the nick of time and sent the Turks reeling back. They were never a threat to Europe again. Austria repaid the favor by participating in the next century in the dismemberment of Poland with Prussia and Russia.

The third invasion is now. More than 10 million men and women of Islamic faith live in Western Europe today. They have not come as armed invaders seeking to take political power. Rather, they are poor people seeking jobs and the good life for themselves and their families and hoping to preserve some of their heritage while they do so.

No one really wants them. In this country an anti-immigrant political party is already part of the government. In other countries opposition has increased dramatically. A cardinal has asked the Italian government to ban more Muslim immigrants. Yet Western Europe, whose low birth rates have created a serious shortage of labor, need them. Like all immigrants the Islamic arrivals--Turks, Moroccans, Pakistani, Algerians--are relegated to the fringes of society. Some of them are involved in crime. Their young are restless and alienated. Their neighborhoods are considered dangerous at night. These descriptions are not unlike the descriptions of the Irish and Italians and Poles in this country in the 19th and early 20th Century.

The official policy is that these immigrants be integrated into the host societies and become good Austrians, good French, good Germans, good Britons while retaining a "humanistic" version of Islam. Leaders of the host societies and of the immigrants have endorsed this goal, perhaps with unrealistic optimism.

According to a copyrighted article in the Paris Herald Tribune, Moroccan youth demonstrated joyously in the Netherlands at the news of the Sept. 11 massacre in the United States. The Dutch Government considered calling out the army to put down the demonstrations. A newspaper poll showed that 20 percent of the Moroccans in the Netherlands were delighted by the murder of so many Americans.

Thus 80 percent were opposed to it, a finding that shows the dilemma of the European governments. Most Muslims in their countries want no part of a holy war against the West. But some, especially among the young people, are angry and cannot be completely trusted.

Europe cannot expel the new invaders, both because it needs them to do the dirty work in European society and because most of them are not criminals. Yet some of them either are or willing to be. And many Europeans hate them--all the while decrying American racism.

At least the European police seem to be able to keep an eye on them. They quickly picked up suspects in France, England, and Germany after Sept. 11. The FBI, stumbling and bumbling as always, had done nothing about a CIA warning concerning two of the hijackers.

Europe and the United States share common problems: how does one deal with immigrants among whose number might be a tiny number of dangerous religious fanatics and at the same time preserve the values that the fanatics like bin Laden wants to destroy. How does one cope with the racist haters from within? Yet if the West can facilitate the integration of Islam, it will be richer and better for having done so.