THERE are ``irreducible differences'' between the French and American commitment to European defense, says Dominique David, secretary-general of the Foundation for National Defense Studies in Paris. ``France takes risks at home. The US takes risks in Europe - in its own interest, but not on its own territory.'' The United States can therefore decide to opt out, he concludes; France cannot.
Going on to describe the French-West German cooperation that Paris cannot opt out of, he says, ``The majority of French public opinion today thinks that French arms should help Germany if it is attacked. ... I think we made a lot of progress since '80, '81, '82 - progress more political than military. Today it is possible in France to say things about Germany and the alliance which could not have been said 20 years ago [when Paris withdrew from NATO's integrated military command]. There has been an important evolution in the political class and public opinion, and in Germany too there has been an evolution.''
Karl Kaiser, director of studies at the German Society for Foreign Policy (DGAP) in Bonn and co-publisher of a new book on French-West German security coordination, would not disagree with this assessment. But he stresses the limitations and sees the bilateral relationship as ``a case of unrequited love - on both sides.''
Both views are valid. Once again the odd couple of France and West Germany are being pushed together, by their fears of American disengagement from Europe. Once again they are encountering some ``irreducible differences'' of their own. But however troubled, the security partnership between two nations that for a century and a half were arch enemies is already one of the great achievements of the 20th century.
That partnership, as Mr. David suggests, is as much psychological as military. That makes it especially tricky for observers to sort out substance from image - and also makes it deceptively easy to belittle the substance that the deliberate image itself creates. An American diplomat describes the approach of President Francois Mitterrand thus: ``The thing that is important is not the military reality, but the political symbol. That becomes reality.''
The latest bilateral flurry is a case in point. Alfred Dregger is chairman of the West German conservative parliamentary group, a longtime supporter of the US, and, until recently, a fan of President Reagan's Strategic Defense Initiative (``star wars''). Last month Mr. Dregger recoiled from US pressures on Bonn to endorse superpower arms control by calling for a security union between Paris and Bonn, with French nuclear weapons pledged to defend West Germany.
Three years ago ex-Chancellor Helmut Schmidt had similarly proposed integrating the French and West German armed forces under a French commander, but in 1984 the time was not yet ripe. By this year, however, it was an idea whose time had almost come. Former Prime Minister Laurent Fabius declared himself in favor of a ``type of German-French confederation'' in which Bonn would take the lead in economics and Paris would take the lead in defense and foreign policy - and might actually extend that sacrosanct nuclear protection to West Germany.
CHANCELLOR HELMUT KOHL, in what some Bonn observers regarded as a splashy initiative to undercut Dregger's radical proposal, immediately broached the more modest idea of forming a joint French-West German brigade. President Mitterrand in turn immediately suggested that such a unit could form the ``embryo of a European conventional defense.''
The military technocrats grumbled about the problems of issuing orders in English, but started groping for ingenious ways to build a single unit whose German soldiers would be subject to NATO command and whose French members most emphatically would not.
What the technocrats missed was the enormous symbolic value of combining forces of the two largest European countries, nations whose mutual suspicions lingered long after their last war ended in 1945. It looks as though the brigade will come into being, and its promoters stress that the key tactical operational concepts of the French and West German Armies are quite compatible.
A bilateral brigade may not commit French ports and airfields to receive essential American reinforcements in time of war. It may not guarantee the crucial depth of field to the front-line country that is a perilously narrow 150 miles wide. It surely will not build up the numbers of soldiers declining from sheer demography in West Germany and from the diversion of conventional budgets to nuclear programs in France. But it will send a powerful signal of enhanced French commitment to defend West Germany to the one audience that matters most, in the Kremlin.
Certainly the movement in bilateral relations is striking. Back in the 1960s the much-heralded French-West German rapprochement actually led to a standoff as President Charles de Gaulle pressed Chancellor Konrad Adenauer to choose between America and France, and Adenauer, not surprisingly, chose superpower America.
There things stood until the early '80s, when controversy over new Euromissile deployments broke out in West Germany and a cultural upheaval in Paris led the intelligentsia there to abandon its fascination with Marxism and turn to belated abhorrence of the Soviet gulag and repressions in Poland and Afghanistan.
The shift in France coincided in West Germany with the rise of a popular antinuclear movement, a recoiling from the hard-line rhetoric in the early Reagan White House, fresh realization by West Germans that they were living in the land with the world's highest concentration of nuclear weapons per capita - and Social Democratic skittishness about adding new American Pershing and cruise missiles to this arsenal.
This divergence between the two countries aroused French concern that the Soviet Union might dangle reunification before the Germans and tempt them into neutralism - and thus remove the glacis, or military buffer zone between France and the potential aggressor of the Soviet Union. Paris therefore strove for closer security cooperation with Bonn that would dampen West German enthusiasm for d'etente, ``anchor'' West Germany in Europe, and avoid its ``drift'' to the East, thus minimizing the dangers of the ``German uncertainties'' and lack of full national identity.
IRONICALLY, the French alarm was expressed by the Socialists, who had finally come into office and toned down their out-of-power radicalism - and chided their West German comrades not, as in the 1970s, for being too bourgeois and anticommunist, but for being too radical and gullible toward Moscow.
President Mitterrand, having recently brought the French Socialists to love the French bomb, now lectured the Bundestag and the West German Social Democrats that they should love the new NATO missiles.
Dominique Moisi, deputy director of the French Institute of International Relations (IFRI), DGAP's sister organization in Paris, terms the French fears ``fantasies'' about what was actually a ``German return to adopt a normal attitude to national identity.''
But however exaggerated they may have been, they impelled Paris to abandon old taboos and act in ways that would have been unthinkable only a few years ago. On the one hand, Paris still sought to some extent to win Bonn over to ``Eurogaullism'' against the US - but on the other hand it let West Germany draw France closer to unannounced pragmatic cooperation with the NATO military command.
With considerable fanfare, the proviso for security cooperation in the 1963 'Elys'ee Treaty of reconciliation was dusted off in the early '80s. The two countries' foreign and defense ministers began meeting several times a year and organized exchanges and joint training for young officers.
France saw to it that the remaining restrictions on West German conventional armament under the soporific Western European (defense) Union were lifted by 1984 (though West Germany wanted to and did remain bound to nonpossession of atomic, biological, and chemical weapons).
Various French officials and ex-officials floated trial balloons suggesting that France's ``vital interests'' could not be confined to soil west of the Rhine (the French-West German border) but really began at the Elbe (the East-West German border), and talked about Western Europe as a common ``defense theater'' that must be embedded in NATO. The biggest bilateral exercises ever staged since France left the NATO military alliance brought 150,000 troops together in West Germany last year, with even larger maneuvers planned for this coming fall.
What Bonn wants out of the relationship at this point is to restore as much automaticity as possible to France's commitment to help defend West Germany in case of Soviet attack; that automaticity vanished when France left NATO's military wing in Gaullist independence in 1967.
Concretely, Bonn wants Paris to discipline its nuclear dreams, return to the drudgery of Europe's urgent conventional requirements, and provide early in any war the operational reserves for counterattack that NATO's thin front line would need. Bonn would especially like to see a strengthening of the French Second Army Corps and First French Army in West Germany, and replacement of their antiquated or nonexistent tanks, fighting vehicles, artillery, and logistical support.
BY contrast, what Paris wants to do is to shield its glacis of West Germany from even the temptation to go neutralist, while still guarding France's nuclear independence and reserving its decision even on common conventional defense until the last minute.
Further, Paris wants to hold open the option of leaping from France's ``splendid isolation'' today to French leadership an integrated Europe tomorrow. That feat would require the support of the West Germans, the most powerful Western Europeans, but ones who are themselves barred from leadership because of the remaining memory of Adolf Hitler.
Moreover, in 1986 France promised publicly to consult with West Germany (time permitting) before firing any of its ``pre-strategic'' nuclear weapons that would land only in Germany. And following last fall's superpower summit in Iceland, one French presidential adviser even told an IFRI conference, according to an astonished fellow participant, that while ambiguity must be maintained in nuclear weapons, in the conventional area the time has come to take big steps toward an integrated command with West Germany along the lines proposed by Mr. Schmidt.
A French officer comments, ``De Gaulle was good for France in 1960. Now I think it's another position that we have to take.''
For the moment the impetus to further French-German rapprochement is there in the German elite's sense of crisis about the American guarantee and the French elite's sense of crisis about potential German neutralism. But is this double urgency enough to make Europe's heartland ``hang together''?
``The dialogue on the political level has become more active than ever before,'' says Bruno Racine, a foreign policy adviser in the office of French Prime Minister Jacques Chirac.
``Relations between both armies have also reached a degree [of closeness] never attained in the past. We have built the basis for further progress.''
But Ingo Kolboom, West German co-editor of the DGAP-IFRI study of German-French relations says it's a ``delicate tightrope walk between French autonomy and German integration.''