NUCLEAR ENERGY, nuclear weapons, the environment and inflation are the issues in West Germany. The political campaigns there are on the same schedule as in this country, moving toward national elections next fall. But the choices are clearer in Germany than here, for German voters already know who the candidates for chancellor will be; the parties have chosen their leaders, and there is nothing like the long American ritual of the primaries. The outer great difference is, of course, that geography and history draw the choices much more tightly for the Germans.

Take, for example, nuclear energy. A lot of Americans wonder whether the country should not stop building power reactors altogether. Helmut Schmidt, Germany's chancellor and a Social Democrat, crisply argues that for Germany there is no alternative to nuclear energy. All of Germany's oil is imported, and it possesses nothing like the huge American reserves of coal. Without nuclear reactors, the chancellor argues, there will be little economic growth of any sort for West Germany. Without growth, there is no way to finance social advances -- either for Germans or for the poorer countries to the south that depend crucially on expanding markets in the industrial world.

The sharpest opposition to the German reactors comes from the environmentalists who have now organized themselves into what they call the Green Party. But the Greens are in an awkward position. If they press their campaign, they might conceivably defeat Mr. Schmidt -- bringing into power a fiercely conserative government led by the irrepressible Franz Josef Stauss. In his skill and his appeal to nationalism, Mr. Strauss occupies a place on the political compass that is, for example, roughly similar to John Connally's in this country.

In much the same way, circumstance constrains the debate over the emplacement of new nuclear rockets in Germany. Chancellor Schmidt observes that you can't negotiate arms control with the Russians unless you have arms. Over the past autumn the Russians attempted to intimidate Germany on the rocket decision, but the tactic failed. There aren't many Germans who would really have wanted it otherwise -- certainly not Mr. Strauss and the conservative coalition that he leads.

But there's good deal of tension within Social Democratic Party itself, where the left wing feels itself isolated from the main thrust of government policy. The left knows that the government will probably win again next year, under Chancellor Schmidt's leadership. It also knows than any attempt to push him toward a more marked socialism would be fatal to the party itself.

Germany's wealth and standard of living have increased enormously during these past 10 years under Social Democratic chancellors. That, paradoxially, has left Germany less inclined than ever to socialist experimentation. Recent experience has apparently confirmed the German predisposition toward a careful pragmatism that assigns very high value to stability. Perhaps it is a general rule of politics that prosperity tends to diminish the appeals of party doctrine and program.