Paris — ''I defend France's interests,'' Jean Marie Le Pen says softly. He smiles, and his blond hair and cherubic face disarm a cautious listener. Then he provokes. ''It is legitimate that French citizens be favored over foreigners.'' By now, the words begin to roll off his tongue with force, finally reaching a crescendo. ''We have to throw out all the illegals,'' he shouts, concluding ominously, ''if we don't, it will end badly.''
A year ago, no one noticed Mr. Le Pen's fiery anti-immigrant rhetoric. Dismissed as fanatic, his National Front Party scored only about 1 percent in the polls.
Today, the same rhetoric is tearing French politics apart. Le Pen is everywhere, drawing huge crowds to his rallies, on the covers of the national newsmagazines, on television - and his party's standing in a series of recent municipal elections is up to between 10 and 15 percent of the vote.
So far, similar national front parties have remained marginal in both West Germany and Britain. But right-wingers in the mainstream parties in both countries have embarrassed their colleagues with racial outbursts. At the recent British Conservative Party conference, for example, an Asian speaker was booed with cries of ''Out, out, out.''
Moreover, in many ways the rise of the extreme right is not the most dangerous aspect of the political debate over immigration.
Even in France, few expect that Le Pen's National Front will overtake the mainstream conservative parties. But Le Pen has succeeded in putting the foreign workers at the center of French political debate.
This success raises the key question: How tough will the established parties have to become to defuse the immigrant issue?
Immigration controls were first enacted in the early 1970s, and today there is a wide consensus that no additional foreigners can be accepted. Both left- and right-wing governments have followed this same policy.
''Open immigration,'' says British Labour Party shadow home secretary Denis Howell, ''is simply not politically acceptable with so many unemployed.''
Today, though, governments are moving beyond simple immigration limits to even tougher, more controversial, rules. German Chancellor Helmut Kohl has lowered from 16 to 6 the maximum age at which Turkish children can join their parents in West Germany. British Prime Minister Margaret Thatcher's 1983 Nationality Act makes it more difficult for Asian and West Indian citizens to have a potential wife live in the country.
''WE feel we have to move swiftly to show that we are making progress on the immigration issue,'' explains Mervin Koler of Britain's Conservative Party. ''This calms potential worries.''
The most striking sign of the need to calm worries has come in France. The Socialist government came to power three years ago pledging to liberalize policy for the foreigners. It amnestied 100,000 illegal workers and ended the previous government's attempt to pay immigrants to return home.
Today, this generosity is long forgotten. Under the pressure of the immigrant backlash, the Socialists have copied their tough predecessors and even outdone them. Border crackdowns have been stepped up, with wives and children often refused entry. Well-publicized expulsions of illegal aliens have been enforced, and a new program to pay immigrants to return home was announced. Immigrants will be offered 40,000 francs ($4,600) and retraining in their native countries.
''We are in war against unemployment,'' explains Georgina Dufoix, minister for immigrant affairs, in reference to the tough policies. ''Our measures are visible and efficient? All the better.''
But are such repatriation programs, a remedy also recently enacted by Germany's Kohl government, actually effective? The toughness may satisfy an increasingly irritated public opinion, easily swayed by men like Le Pen who proffer the false equation that ties the numbers of unemployed to the numbers of foreign workers.
Still, past French and German paybacks have had only minimal success, and officials admit that new programs will not resolve the immigrant problem.
''We are only expecting about 20,000 Turks to take advantage of the new offer ,'' says Jurgen Haberland of the German Labor Ministry. ''This is a limited program, a limited solution.''
Apart from a decision to summarily expel the immigrants, the flow may be slowed, but it cannot be reversed. So far, only Switzerland has refused to renew temporary work permits for guest workers. Other European countries cannot act too harshly - because of their constitutions, their post-colonial obligations, or Common Market regulations.
In this context, experts fear schemes to send workers home are dangerous panaceas. They muddle, even hide, the hard truth that the foreigners are here to stay.
''I call it the 'myth of the return,' '' says Muhammad Anwar of Britain's Council of Racial Equality. ''These people can't go home, economically and socially. They are morally German or French, even if not technically. Europe must face up to this reality.''
SIGNIFICANTLY, on this point Britain stands apart from its cousins across the English Channel. Britain's nonwhite immigrants came from the Commonwealth, and as descendants of the empire, they are citizens. Despite the Thatcher government's conservative tendencies and continuing racial tensions, this granting of citizenship represents a significant step toward defusing the immigrant time bomb.
''In France and Germany, guest workers aren't French or German, and like the word says, they're guests who can be kicked out,'' explains Aaron Haynes of the Council of Racial Equality. ''Our problem here in Britain is a straight race problem.''
On the Continent, therefore, politicians debate the problem of ''foreigners.'' Mention the same euphemism in Britain and a cry of anger is heard.
''Don't use that word,'' orders Denis Howell. ''We talk about community relations.''
The difference is important. In Britain no one talks about sending the immigrants back home. Instead, the political parties are working hard to satisfy minority interests in order to win minority votes.
''Of my 64,000 constituents, 25 percent are Asian and 30 percent West Indian, '' Mr. Howell says. ''I have to take care of them - or the Conservatives will get them.''
The result, according to Howell, ''is that now not even Mrs. Thatcher considers an expulsion policy. Ethnic groupings are accepted as a political fact of life.''
Continental Europe seems unable to make this leap of faith and accept similar ethnic politics. At present, in both Germany and France most children of immigrant parents are not citizens. Double nationality exists in France, but not in Germany, and even the most liberal in both countries are hesitant to naturalize most of the foreigners.
''It would be difficult to recognize double citizenship here,'' says Rudolf Dressler, the German Social Democratic Party's spokesman on immigrant affairs, and a strong critic of the Kohl government's harsh measures. ''And there is no question of changing the Constitution to let the foreigners vote.''
The danger with this hesitancy is that men like Le Pen will be able to exploit it. The French right-wing leader aims to gain at least 10 percent of the vote in the coming June elections for the European Parliament. If he does, his party could have a potential role as a power broker in the 1986 legislative elections by forming a coalition with either of France's mainstream conservative parties.
In Germany, despite the tension over immigrants and the controversy over the Kohl government's tough policies, there is no such immediate danger. Some worry, however, that in the long term the issue could pose a serious political threat.
''So far, we've kept this off of the front pages because of our sensitivity over fascism,'' says Gunter Lochner of the ministerial working group on foreigners. ''But we need to accept that our society will become multiracial. Like Great Britain, our political understanding has to grow.''
Next: First steps toward forging multiracial societies.