By deciding at the weekend to extradite three Basque refugees to Madrid, Socialist President Francois Mitterrand ended France's policy of granting Basques political exile and sent a strong statement of support to Spain's Socialist government.
The President's choice was extremely difficult, top French officials explained. Send the three Basques back to Spain and Mitterrand would face certain violence on the French side of the Pyrenees. Or refuse and, as an official said, ''signal that we don't consider Spain a democracy.''
Traditionally, France has refused to return the Basques, claiming they would not receive a fair trial in autocratic Spain. Even after democracy was established in Madrid, the French continued this policy in return for what amounted to an unwritten agreement that the separatists would avoid trouble with the large Basque population in France.
This conciliatory attitude changed last winter. The bloodshed then spilled over the border when an organization called the Anti-Terrorist Liberation Group killed eight suspected Basque terrorists living in France.
After the murders, the separatist organization known as ETA appeared for the first time on French streets, with marches and Irish Republican Army-style funeral ceremonies.
French authorities responded by removing from the border area 60 suspected separatists. France also began deporting militants wanted by Spain to the Caribbean.
There was a temptation for the French to do the same in the present case, and they did decide to deport to the West African nation of Togo four men wanted on nonviolent crimes rather than extradite them.
But the other three were wanted on charges of murdering Spanish policemen. As a French official explained, ''How can you say you are a country of law and then not follow the law in such a serious case?''
The reasons for the decision were political as well as moral, however. Refusal to extradite was a constant thorn in relations between Madrid and Paris, and for strategic and commercial reasons, France wants to link Spain closer to the rest of Western Europe, both in the European Community and militarily.
On both counts, Spain has seemed hesitant. Prime Minister Felipe Gonzalez came to power two years ago promising a referendum on continuing its membership in NATO's military alliance.
More recently, he threatened to break off negotiations that are supposed be completed by the end of the year for Spain's entrance in the European Community's economic association - largely because of a dispute with France over agricultural subsidies.
Spanish attitudes will not be completely reversed by France's new willingness to extradite Basques. But French officials hope it will at least make for greater trust between the two governments, and it may just do that. Spanish reaction to the decision, noted here at great length, was almost universally positive.
The Basques, of course, were not celebrating. Violent demonstrations broke out Sunday and Monday on both sides of the border. At time of writing the number of casualties was not yet clear.
For the French, the real danger is that ETA may step up its activities north of the Pyrenees. Security forces in the region have been put on alert. French officials say they will have to stay prepared for a long time.