AIX-EN-PROVENCE, FRANCE — Asked about the number of foreigners living in Europe, sociologist Jocelyne Cesari throws up her hands. ''I'd sure like to know,'' she says, laughing ruefully.
In Brussels, Sophie Petzell, spokeswoman for the European Union commission that watches immigration, gives the same laugh. ''Who knows?'' she replies.
For the European Union, Austria, and Switzerland, foreigners with legal residency likely number between 15 million and 20 million. More than one-third are Muslims from North Africa, Asia, and Turkey.
But all figures are misleading. First, no one can count clandestine immigrants. Depending upon which official study is consulted, the number in Italy is a fraction more - or three times more - than the 1 million legal ones.
In Spain, according to one intergovernmental report, 3,377 Algerians were registered residents in 1993. That year, the document adds, Spanish police arrested 8,544 Algerians for criminal activities.
Jean-Claude Barreau, who advises the French Interior Ministry, says France alone discovers 50,000 illegal immigrants a year, a fraction of the real total. Second, ''foreigners'' are difficult to categorize in the European Union, which is made up of 15 member states with varying nationality laws and colonial histories.
For many French, ''immigrant'' is a code word for North African, including Algerian veterans of France's war in Vietnam who have been citizens of France since birth.
France confers citizenship to anyone born within its borders, including its overseas outposts in the Caribbean, Pacific, and Indian Ocean. German citizenship requires German blood, or a difficult process of naturalization. Britain's laws are complex, designed to stem a flow of immigrants that followed the end of its empire.
Immigration figures include not only people of color but also Caucasians. Still, immigrants from Eastern Europe and the former Yugoslavia often face discrimination in places where local people blame them for economic problems.
According to the Paris-based Organization for Economic Development and Cooperation, Germany has the largest legal non-European Union population, with 5.3 million. That includes almost 2 million Turks and nearly 1 million former Yugoslavs. France is next, with 2.3 million. Of those, Algerians, Moroccans, and Tunisians make up 60 percent. Britain has 1.3 million legal immigrants, about one-quarter of them from South Asia.