TWELVE million workers from the third world poured into Europe in the booming 1950s and '60s to run the Continent's factories and sweep its streets. In the recession-ridden 1980s, these workers are no longer welcome.
Extremist violence in the ghettos of London's East End, Cologne's Weidengasse , and Paris's La Courneuve is the most visible sign of this rejection. But the growing anti-immigrant feeling reaches far beyond these physical explosions, often to the center of the Continent's economic, social, and political institutions.
The immigrants take our jobs, many charge. They bankrupt welfare budgets, they cause crime, and their children ruin the schools.
''Urgent action is needed if (racial disadvantage) is not to become an endemic, ineradicable disease threatening the very survival of our society,'' commented Lord Scarman, in his report on the 1981 riots in the Brixton section of London that left more than 300 people injured. Thirty-six percent of Brixton's residents are black, and the area has both high unemployment and substandard housing.
A September report of the Council of Europe drew the same ominous conclusion for the entire continent, warning, ''Large concentrations of migrant workers have created an explosive situation.''
Instead of urgent action, though, confusion reigns over what to do with the foreigners. Should they be sent home? Governments in France and West Germany are now paying foreigners to leave.
Or should they become citizens in their new homes? The same governments in France and Germany cite such integration as a goal.
''We have too many foreigners to integrate, and yet we can't kick them out,'' laments Walter Bruckman of Germany's ruling Christian Democratic Union. Like many other Europeans, he sees his society as a homogeneous entity, saying, ''We are not a classical immigration country like the United States, taking different people in from all over the world.''
This explains why, except in Britain, the workers are ''guests,'' not citizens. When companies recruited them, they were given one-year contracts. No families came. When the year was up, it was assumed a worker would pocket his earnings and return home.
''Of course, it didn't work out that way,'' says Jurgen Haberland of the West German Interior Ministry. ''The foreigners didn't want to leave to face unemployment in their native countries. And employers didn't want to train new workers every year.''
SO the immigrants dug into their adopted homes. Wives came to join husbands. Entire families were reconstructed - and presto, Europe soon became multiracial, with huge, new nations within nations. Berlin now is the second-largest Turkish city in the world. Paris's La Courneuve is only one of the city's many North African ghettos; London's East End only one of many Asian or West Indian ghettos.
As long as the economic boom continued, governments let the immigrants stay on - and their numbers increased. Then came the l973 oil shock, followed by hard times and high unemployment. Every European government responded by banning arrivals of new ''guests.'' Later, programs were instituted to pay workers to return home.
But the influx was only slowed, not stopped. Illegal immigration, asylum applications, and a high birthrate kept the foreigners' numbers rising. In Britain, the 1981 census counted 3.37 million immigrants, an increase of 13 percent in a decade. In West Germany, the Labor Ministry reports, the numbers swelled from 3.9 million in 1973 to 4.5 million this year.
In all, nearly 8 percent of both the French and German populations now is foreign, and nearly 6 percent of the British population is foreign born. The high immigrant birthrate makes demographic projections even more striking. Today , one child in six born in Germany is not German. If the trend continues, by the year 2000, the Labor Ministry forecasts, Germany will be home to 7 million foreigners, some 11.2 percent of the population.
These numbers constitute a social time bomb behind the anti-immigrant upheaval. ''Some people find they are swamped,'' British Prime Minister Margaret Thatcher said in 1977. Right-wing parliamentarian Enoch Powell has put the danger much more bluntly, predicting ''rivers of blood.''
Mr. Powell's statement exaggerates - but if there is not yet a river, there is at least a disturbing stream. A 1982 British Home Office report found that Asians are 45 times more likely to be attacked than whites. And sometimes, as the riots a few summers ago in Brixton and Liverpool show, the immigrants fight back.
Racial violence also plagues France and Germany. Statistics are not so carefully compiled, but well-publicized incidents such as the murder of 10 -year-old Toufik and Cologne's neo-Nazi outrages abound. Thankfully, though, immigrant reaction has rarely gone beyond peaceful demonstrations.
''Faced with these provocations, so far, our immigrants have been patient,'' says Francoise Gaspard, author of the recent book, ''The End of the Immigrants.'' ''How long can this last?''
At first glance, it is surprising that the immigrants should pose such a problem. Mass migration, after all, is nothing new in European history. Religious, economic, and political crises have uprooted people for centuries: Huguenots to Germany, Poles to France, and most recently, millions of Spaniards, Portuguese, and Italians to factories in the north.
Each wave met resistance, but in most cases the immigrants made out well. They were European, white, and Christian. They came to make their lives anew, not as temporary migrants.
As such, they did not threaten European society with the vision of the American ethnic kaleidoscope. The Italians dissolved into Germans, the Poles into Frenchmen.
The recent, largely non-European immigrants are different. Most are Muslim and many black: In either case, they come from alien cultures that often bore the brunt of imperialism.
''It's very hard to cut away from the empire,'' explains Aaron Haynes of the British Council of Racial Equality. ''This system is devised for a white, homogeneous society: It can't deal with difference.''
DIFFERENCES do foster tension. Petty as it sounds, loud music and smelly foods often spark the most anger. Scotland Yard officials say loud reggae music, played by West Indians, has caused innumerable spats in London. French officials say cooking odors from the apartments of North Africans have prompted numerous complaints. Turks face similar problems in Germany.
''Many Germans just don't try to understand,'' says Margerete Jenke, a Cologne social worker. ''During Ramadan, we think they are going to make sacrifices on their balconies.''
These social misunderstandings are exacerbated because the immigrants are concentrated in specific urban neighborhoods.
Take crime. Studies show that immigrants commit the same number of offenses as native citizens of their age and income level. But because the immigrants are predominantly young and poor, their neighborhoods are associated with delinquency and insecurity.
''It creates a certain Harlem effect,'' says Christian Rosenmoller of the German Ministry of Labor. ''When people are scared, there is tension.''
Another problem is schooling. In certain urban areas, immigrant children make up the majority of students in the public schools - raising fears that they lower the educational level.
''I have four children,'' says Denis Howell, the British Labor Party's deputy shadow home secretary and member of Parliament for Birmingham. ''When the first went to school in the late 1950s, there were only two or three colored faces. For the second in the early '60s, there were 12 out of 30. For the third in the late '60s, there were almost three-quarters. And now with my last, there are only two or three white students.''
''This causes tensions,'' admits Mr. Howell, a staunch supporter of minority rights.
These attitudes show that racism exists apart from economic considerations. But it is the recession that has brought the clash of cultures to the boiling point. Only after the first oil shock was the immigration problem first recognized. Now, with Europe mired in economic stagnation, the most serious charge leveled at the foreigners is that they take jobs from native citizens.
''Two million unemployed equals 2 million foreigners'' is the common slogan. The charge is false, because all studies show that the immigrants do dirty work natives would not take on.
FOR example, a French government study showed that for every 200,000 fewer foreign workers, only 13,000 natives would receive jobs. Meanwhile, a German study completed for the town of Dusseldorf reported that if 75 percent of the city's foreigners were to leave, the city's public transport would stop, its hospitals and homes for the aged would close, and electric power production would be threatened.
Nonetheless, the rallying cry equating unemployment with foreigners is gaining volume. In a recent strike over layoffs at France's Talbot car company, immigrant workers facing layoffs battled with nonimmigrant workers. Such eruptions can be expected to increase as modernization and automation of European factories threaten more and more jobs of unskilled, assembly-line workers - many of whom are foreigners.
Politically, France's extreme right has played on this tension over dwindling jobs and grown dangerously large. Throughout Europe, repatriation schemes are once again in vogue, and campaign debates about the immigrant problem are increasing.
''Our country is experiencing a most dangerous revival of political fever,'' writes Francoise Gaspard. ''It is the unexpected reappearence of racism.''
Next: The effect of racism on European politics.