French President Valery Giscard d'Estaing and West German Chancellor Helmut Schmidt agreed today to use their close ties, in the words of the French leader, "to make the voice of Europe heard" in the world.

Ending a week-long state visit by the French president to West Germany, the two leaders said, however, that they left undiscussed one of the central new elements in their relationship -- France's intention to deploy a neutron warhead.

The French-West German alliance has become Europe's most influential axis. This week, during Giscard's visit -- the first state visit by a French leader here since Charles de Gaulle came in 1962 -- other Western allies were watching for signs of further cementing of this bond, particularly if it were to mean loosening of ties with the United States.

Giscard's announcement two weeks ago that France is considering deployment of the neutron weapon suggested a new dimension to the Bonn-Paris relationship. The device -- a limited-blast, enhanced radiation" weapon to be used against advancing Soviet tanks -- would logically be targeted for use in West Germany.

The French decision raised a number of strategic concerns in Washington and other NATO capitals since the introduction into Europe of a new nuclear weapon by France, which does not belong to the Nato military structure, is likely to complicate alliance defense planning.

Aides to both Schmidt and Giscard said the issue was not taken up by either leader, nor by their defense ministers. Giscard told a press conference, "We did not in any way study or consider a modification of the existing military relations between Germany and France."

While the reason for this appeared to be the newness of the French decision, it also seemed to underline the practical limits of the Bonn-Paris alliance, just as Giscard has been seeking to use it to assert French-German leadership of an independent Europe.

West Germany, still heavily dependent on the U.S. nuclear guarantee for its security, has been reluctant to distance itself too far from Washington --although Schmidt and Giscard are known to share a low confidence in President Carter's leadership. Bonn can be expected to move very cautiously in planning new defense strategy with Paris.

West German officials tried this week to counteract the strong impression generated by Giscard's visit of a Bonn-Paris power axis operating in competition with Washington. Aides to Schmidt said they do not see Bonn confronted with any choice between Paris and Washington. They stressed that Bonn had taken no new policy directions as a result of Giscard's trip.

The Franco-German relationship already has reached a comfortable, extensive and powerful working level. Two years ago it masterminded the creation of the European Monetary System, intended to shield European currencies from the volatile swings in the value of the U.S. dollar. This year, French and West German officials were instrumental in solving the European Community's budget crisis involving Britain.

Schmidt and Giscard, whose friendship has enhanced ties between their countries, now see one another on the average of once a month.

Giscard's purpose here this week appeared to be to make a public declaration of this fact and to nudge Schmidt into a closer relationship. At virtually every stop, the French leader delivered the same message as the one he gave in the town of Kassel.

"Our two countries have a special responsibility," he said, "to give back to Europe its influence in world affairs, after the years of effacement because of the world wars."

He avoided big cities, touring through smaller towns instead, where the contact could at least look more personal.

But watching him handshake his way through the provinces, it seemed he was more involved than was his audience. The popular German reception given him, while friendly, lacked the enthusiasm shown DeGaulle when he came 18 years ago.

Some of this reserved reaction is simply the result of a long historical memory. Germans and the French are instinctively suspicious of each other. The modern-day alliance between them has grown more out of necessity than deep kinship.

Giscard was trying to push the relationship into a new phase. The phase of reconciliation started by De Gualle and West German chancellor Konrad Adenauer was over, he said, and the phase of joint action had begun.

This call by De Gaulle's successor, however, contrasted strikingly with the tone set at the beginning of the new Franco-German relationship.

Then when the French general told the Germans, "You are a great people," it was perceived largely as a grant of pardon and respectability for a defeated country that had placed itself outside the community of nations.

West Germany clearly needed French support for its reacceptance -- more than France needed the Germans. Today, things are different.

As French observers noted during the Giscard trip, it is France now that needs to couple itself with West German power to make itself a credible force on the world scene. The tables appear turned, with France seeming to need Germany more than Germany needs France. Giscard, who does not hesitate to make critical remarks about the United States, Britain and the Soviet Union, never utters any public criticisms of West German policy.

As it has evolved, the two nations' political relationship has turned out to be competitive as well as cooperative. This was especially evident recently when Giscard took the initiative from Schmidt by rushing to meet Soviet President Leonid Brezhnev in Warsaw while the chancellor was still planning his own visit to Moscow.

West German officials still seemed irked by Giscard's hasty move. They were also disappointed by France's failure to join in the Olympic boycott. Such aggravations could well deepen as Bonn and Paris continue to pursue their special relations with the Soviet Bloc.

The respected West German weekly Die Zelt said this week that Giscard's repeated advocacy here of a Franco-German "community of destiny" is "more of a dream than an attainable goal."

Still, the key factors that have fostered closer ties between Paris and Bonn in recent months -- uncertainty about U.S. leadership, a wish for greater European assertiveness, the Schmidt-Giscard friendship -- are likely to remain in force for some time.

At a joint press conference today, Schmidt endorsed Giscard's call for a stronger Europe in order to preserve the East-West balance of power. He said he welcomed France's decision to modernize its independent nuclear force by introducing the so-called neutron bomb.

"We agree that there must be an adequate counterbalance in Europe to the extraordinary military power of the Soviet Union, Schmidt said, adding that each West European country should make a specific contribution.

The only concrete new agreements signed here were to ease student exchanges between France and West Germany. The two nations agreed that their next semiannual summit meeting would concentrate on intensifying cultural and educational exchanges.