PARIS, SEPT. 21 -- Behind the mutual flattery and toasts of eternal friendship that suffused talks this week in Munich between their two leaders, France and Germany are confronting a difficult phase in a relationship that has for decades been the driving force of European unity.

West German Chancellor Helmut Kohl and French President Francois Mitterrand said in a joint declaration Tuesday that "our two countries will continue to be the motor of European construction." But in recent interviews in Paris and Bonn, officials of both governments have revealed fresh anxiety about diverging interests. The differences are appearing amid new political and economic forces unleashed by the collapse of East European communism, a vanishing Soviet military threat and a crisis in the Persian Gulf that has doubled oil prices and raised the specter of global recession.

As the two Germanys prepare to unite and the center of gravity for their 80 million inhabitants shifts toward Central Europe, France fears being shoved to the Mediterranean periphery and losing its role as a balancing force between East and West.

French officials say they are troubled that despite the soon-to-be-united Germany's dense web of commercial interests entwining it with Western partners, German preoccupation with melding two states into one and nurturing a new friendship with the Soviet Union may distract it from moving boldly toward European economic and monetary union. Despite Foreign Minister Hans-Dietrich Genscher's advocacy of a rapid timetable for monetary union, German financial leaders are apprehensive about risking the stability of the mark at a time of ballooning German unification costs.

The French Foreign Ministry is seeking feverishly to prepare the first treaty of friendship with the Soviet Union by a Western nation, to be signed when Soviet President Mikhail Gorbachev visits France in early October. But the pact, especially in the area of economic and technological aid, seems destined to pale in comparison with accords to be signed next summer between Germany and the Soviet Union that will establish a new epoch of political, military and economic cooperation between two nations.

In Bonn, officials say Germany's sense of dynamism and excitement about a new era contrasts with the drift and lassitude they see afflicting France's Socialist government in the 10th year of Mitterrand's presidency. They complain that the French have failed to respond positively to their initiatives for a joint policy toward Eastern Europe and enhanced powers for the European Parliament. They attribute such inaction to French recalcitrance about ceding sovereignty and the lack of any blueprint about how to achieve Mitterrand's vision of a European confederation.

"We know it would be a mistake for us to insist on the dominant role in building a new European order because it would frighten our neighbors," a senior policy-maker said in Bonn. "So this should be a great opportunity for France, because a united Germany cannot afford to say no to any initiatives for greater European integration. But when we propose ideas with any content, the French are reluctant to go along."

Kohl's advisers say the absence of any personal electoral considerations in Mitterrand's final presidential term should encourage him to make a bold leap toward European union.

For their part, French officials at the foreign and defense ministries contest the view of unalloyed German allegiance to the cause of European unity. Also, they say, democratic changes over the past year in Eastern Europe require a period of cautious reflection about the future course of political integration.

Moreover, it will be necessary to see how new legislatures in Central Europe as well as the West respond to calls for supranational institutions and the suppression of the nation-state. French diplomats stressed that it is unclear whether even an ardent Europeanist like Kohl will persuade German voters who have dreamed of unification and the departure of occupation forces for more than four decades to cast aside their newfound sovereignty and accept that their political destiny will be decided in Brussels.

Over the next four years, all Soviet soldiers are expected to leave German soil, Britain's Army of the Rhine will probably also depart, and American troops may be reduced to 70,000 or fewer. Germany itself has promised to cut its combined defense forces, East and West, from 600,000 to no more than 370,000 men.

The Germans saw the Munich summit as an important opportunity to breathe new life into the notion of a common European army built on joint French-German units. But even though Kohl managed to persuade Mitterrand to keep options open in the future, France decided to proceed with plans to withdraw half of its 51,000 troops from Germany over the next two years.

French officials said their government is under intense pressure to cut its forces abroad to meet a commitment to reduce defense spending this year by 10 percent and cut troops by at least 40,000 in the next few years. Mitterrand has said "it would be logical" that all French forces would be removed from Germany within four years.