WEST GERMAN governments always collapse in slow motion. Chancellor Helmut Schmidt's coalition began to fall months ago, and the walkout by the smaller of the two partners was preceded by long and public quarrels between them. There is no single great issue on which it all turns, nor does the fall of this government seem to foreshadow any dramatic change in German policy. It is a case of a government that, eventually, wore out.

Bonn is in a state of mind, a spirit, reminiscent of Washington toward the end of a two-term presidency. There are no new questions, and no new answers. Since Mr. Schmidt's Social Democrats came to power, the United States has had four presidents, and France has had three. Mr. Schmidt has been chancellor for nearly eight and a half years, longer than any postwar American president has served. Most of the people in the higher offices in Bonn are physically tired. The smaller party in the coalition, the Free Democrats, put the Social Democrats in office 13 years ago by switching from their earlier alliance with the conservatives. But the Free Democrats' strength has been declining for some time, and, fearing extinction, the party is now thrashing wildly about in its search for a route to survival.

All of that probably means early elections. The last time West Germany held elections ahead of the normal four-year rhythm, in 1972, was a triumph for the Social Democrats. Willi Brandt had just negotiated the peace treaties with Poland and the Soviet Union. The economy was growing fast, unemployment was under 1 percent, and the new government had been able to carry out a series of social and educational reforms.

Today, in unhappy contrast, relations with the East have settled into a sullen antagonism. Poland is under martial law, and neither Germany nor anyone else can do much about it. Foreign policy debates revolve mainly around nuclear weapons, which tend to split the Social Democrats among themselves. The economy, like the American economy, is deep in recession, and the social benefits promised in the early 1970s turn out to be more than the 1980s can pay for.

Germans, perhaps more than Americans, seem oppressed by a claustrophobic sense of no real alternatives to present policy. One response has been the rise of the environmentalists, the Greens. You would be incautious to cheer them on as the party of fresh air, etc. They represent a romantic reaction of a particularly unhelpful kind. Most of them are committed to refuse to share the responsibility to govern. But in the next election, whenever it arrives, quite a few of them are likely to get elected to the Bundestag -- enough, conceivably, to hold a balance of power.