Why France will eat 'le hamburger,' but can't swallow 'le data'

Just after Valery Giscard d'Estaing was elected president in 1974, he gave a press conference to foreign journalists in English. But in Socialist France he would have spoken French.

''Giving that speech was a tragedy,'' says Bernard Cassen, the new director of the Socialist government's office promoting French as a scientific language. ''A French president should only speak French.''

Francois Mitterrand agrees. He refuses to use his minimal English in public and frowns on his ministers giving press conferences in a foreign language.

This change in policy is only one way the Socialists are reemphasizing linguistic purity. Some of the others:

* Jean-Pierre Chevenement, the minister of research and industry, has decreed that his ministry will no longer provide funds and technical support to international gatherings here in English.

* Jack Lang, the culture minister, has toyed with the idea of putting a quota on music and films in English.

* Claude Cheysson, the foreign minister, is beefing up France's language program abroad, which already is the world's biggest relative to France's population.

France's problem is that its language is losing out worldwide to English. There are 90 million native Francophones, compared to the estimated 350 million Anglophones. American economic, cultural, and military dominance makes English the world's most popular second language.

For a long time English has been invading French daily life - words like le drugstore, le baby-sitter, and le hamburger.

Snobbery and laziness are two reasons for the encroachment of this so-called Franglais. But also in many modern technical fields the lack of a French word has forced Frenchmen to turn to English. Hence the verbal shorthand for the French appareil a reaction becomes, quite simply, le jet.

So what are Frenchmen, proud of their tongue and eager to safeguard it as a major world language, to do?

Since 1972 various government ministries, coordinated by the High Committee of the French Language, which is attached to the prime minister's office, have published French substitutes for many of the popular Anglo-Saxon terms here.

Under the Giscard administration, though, the intensity of the language battle was toned down, says Alain Fantopie, the high committee's director for the past 12 years.

''The Socialists are much more serious about defending and promoting French, '' he says.

The philosophy behind the renewed efforts is not to drive out all English words, but just to change those that the authorities feel don't go well in French. For instance, le hamburger will stay because its meaning is clear and its easy to pronounce, but ''data processing'' becomes informatique.

''I can't even say 'data processing,' '' Mr. Fantopie says, indeed stumbling over the word. ''We are trying to give Frenchmen confidence in their language by making it clearer and more comprehensible.''

But some Socialists push the point further. Research Minister Chevenement's proposed boycott means that native scientists will have to address scientific congresses here in French - even if the majority of the listeners are foreigners.

''Unless French becomes an accepted scientific language, French citizens will continue not to understand science, and our scientific production and quality will remain limited,'' Mr. Cassen explains.

This reasoning does not convince many French scientists. ''If I publish in French, no one will read me,'' physics professor Marcel Froissart complains. What will happen if all future conferences in France must be held in French? ''There will be no more conferences here,'' he answers bluntly.

Similar complaints have forced Culture Minister Lang to scrap his proposals to limit American music on the radio and American films on television. Surveys showed that radio and television would lose too many listeners and viewers.

Still, the Socialists remain committed to their program. Deliveries of audiovisual material for teaching French around the world by the 30,000 French teachers now abroad have been stepped up; so has assistance to the more than 2, 000 privately funded branches of the Alliance Francaise.

''We spent more money than anyone in the world per capita on this even before the Socialists, but now we are making still more of an effort,'' a Foreign Ministry official said.

''We realize we can't beat English,'' Fantopie says. ''But we want to make sure the survival of French as a strong regional language. After all, if everybody spoke English, the world would be so dull.''