Premier Jacques Chirac said on Saturday that France would respond immediately and unreservedly to aid West Germany in the event of an attack on France's neighbor.
His pledge, in a speech at the Institute for Higher Studies on National Defense, was the first time a French leader had so clearly committed his country's forces to the defense of its neighbor.
France has shown concern about U.S. commitment to European defense since the signing on Tuesday of the U.S.-Soviet treaty scrapping intermediate-range nuclear missiles.
"There cannot be a battle for Germany and a battle for France," Chirac said. "Who can now question, in the hypothetical case of West Germany being a victim of aggression, that France's commitment would be immediate and without reserve?"
He did not spell out whether France's nuclear force would be used in defense of West Germany but the context of his words suggested a wider role for its independent deterrent.
There are fears in France that the United States might withdraw its nuclear umbrella from Western Europe in the aftermath of the signing of the U.S.-Soviet treaty on intermediate nuclear forces.
Chirac said he welcomed the accord but cautioned against excessive or premature optimism. He said European countries must work more closely together to defend themselves.
France has an independent nuclear strike force, including battlefield weapons, while West Germany is banned from having such arms. France has 50,000 men stationed in West Germany.
Under traditional French defense doctrine outlined by the late Gen. Charles de Gaulle, only an attack on French territory would trigger an automatic response by the country's nuclear and conventional forces.