West German Foreign Minister Hans-Dietrich Genscher met with President Reagan yesterday and said afterward that the United States has Bonn's full support to press the Soviet Union for elimination of all medium-range nuclear missiles based in Europe.

Talking with reporters after the White House meeting, Genscher said the two governments agree that the "zero-option" plan advocated by the United States in the Geneva negotiations, which resume today, offers "the best solution for Europe, for West Germany and for the West as a whole."

The U.S. proposal, also called "zero-zero," calls for the Soviet Union to dismantle its intermediate-range missiles in exchange for abandonment by the North Atlantic Treaty Organization of its scheduled deployment of new-generation U.S. Pershing II and Tomahawk missiles in Western Europe. These missiles would be able to strike deep inside the Soviet Union.

While expressing hope that the Geneva talks will produce "a concrete result" satisfactory to the West, Genscher stressed that NATO must be ready, if the Soviets are not forthcoming, to begin deploying the U.S. missiles on schedule in December.

"It must be clear that the date of schedule for deployment would not be changed, and no doubt should be cast about delay of that date," he said.

With those words, he appeared to be aligning himself relatively firmly with West German Chancellor Helmut Kohl, the most unequivocal supporter of the U.S. position among NATO leaders. Genscher's Free Democratic Party is the junior partner of Kohl's Christian Democrats in the Bonn government, seeking a new mandate in the national elections scheduled for March.

The opposition Social Democrats, reflecting strong West German sentiment for disarmament, have indicated that they would like the United States to ease its negotiating position. They also have said that, if they win the elections, they will defer a decision on whether to allow deployment on German territory until they have assessed any Soviet proposals and the U.S. response.

Genscher, whose party is in danger of failing to retain its representation in parliament, has talked of a possible "interim solution." That, in turn, has raised questions about whether he and Kohl are fully in accord in supporting the U.S. stance.

Yesterday, however, he insisted that his position is fully consistent with the two-track decision made by NATO in December, 1979, when it agreed to go ahead with deployment while seeking negotiations with the Soviets aimed at producing a result satisfactory to the West.

He declined to be specific about what a satisfactory "interim solution" might involve, but said he unequivocally does not favor any agreement that would see NATO surrender the deployment option in exchange for a partial Soviet reduction that would leave Moscow with a "monopoly" of medium-range missiles.

"The result must be equitable and balanced. That's why I say no to a unilateral zero-option for the West," he said. "The zero-zero result is the best obtainable objective, and we must not lose sight of it. We also are committed to the two-track position, and we must examine other possibilities in the light of concrete negotiating results. An answer can be given only when we know what a concrete result means."

He also disputed the idea that the United States should not make new proposals in Geneva until after March because it might influence the election. "What to do and when depends entirely on the negotiating situation, and we do not want it linked in any way to the German elections," he insisted.