France strengthened its defense cooperation with West Germany today by agreeing to establish formal consultation procedures for the use of French tactical nuclear weapons or conventional forces on German soil in the event of war.

The agreement was announced at the end of a two-day meeting here between President Francois Mitterrand and West German Chancellor Helmut Kohl. Defense experts said it appeared to mark an evolution in French strategic thinking, which in the past had stated France's willingness to use nuclear weapons on German soil in deliberately ambiguous terms.

The agreement today reflects an explicit willingness to use tactical nuclear weapons in defense of West Germany against attack by the Warsaw Pact forces.

Official French military doctrine, as enunciated by the late Gen. Charles de Gaulle, has emphasized the idea of a "national sanctuary" defended by an independent nuclear deterrent known as the force de frappe.

France withdrew from the integrated military command structure of the North Atlantic Treaty Organization in 1966.

A joint Franco-German state-ment stopped well short of a "dual key" arrangement, as proposed by some strategists, which effectively would have given Bonn the power to veto French military decisions af-fecting West Germany. The statement said that the right to take operational decisions remained exclusively with the French president as the commander in chief of the French armed forces.

French military experts said that the consultation procedures were similar to those already worked out between West Germany and full NATO members such as the United States and Britain.

"It is politically important for the Germans and marks another step away from the doctrine of France's absolute independence, but whether it will make much practical difference is another matter," said Pierre Lellouche, a military specialist at the French Institute for International Relations.

Today's agreement envisages the establishment of a hot line between a French president and a West German chancellor that would allow them to consult with each other instantaneously in the event of a military threat to West Germany.

"We have in the past outlined such projects. But we had not yet written them down in black and white," Mitterrand said at a news conference.

Other measures agreed upon today include a joint officer training program, the exchange of diplomats and operational cooperation involving France's 47,000-man rapid deployment force. The two governments already have announced their intention to hold the largest joint Franco-German military exercise since the end of World War II, involving 150,000 troops, later this year.

France's tactical nuclear weapons, which are covered by today's agreement, include Mirage and Jaguar fighter bombers equipped with medium-range air-to-ground nuclear missiles as well as Pluton ground-to-ground missiles. The Plutons are due to be replaced by 1992 with a new generation of much faster Hades rockets that will have a range of more than 200 miles with a capability of carrying enhanced-radiation neutron warheads.

In reply to a question, Mitterrand today reaffirmed his intention to proceed with the construction of neutron weapons unless the two superpowers sharply reduced the size of their nuclear arsenals.

The consultation agreement does not cover France's strategic weapon force, largely based on nuclear submarines, which is designed to provide a French president with the option of massive retaliation in the event of a Soviet attack against French territory or "vital interests." What constitutes France's "vital interests" -- and whether they would be jeopardized in the event of a Soviet attack on West Germany -- never has been precisely defined by French strategists.

With just over two weeks until France's legislative elections, opposition leaders have endorsed the Socialist government's attempts to strengthen West European defense cooperation.