THE SUPREME COURT has sensibly concluded that legal and political advocacy groups cannot require the federal government to help them raise funds. For the moment the question of excluding such groups from the government's annual Combined Federal Campaign may still not be settled -- a lower court still has to decide what was this administration's intent in ruling out advocacy groups. Ultimately, it should be possible to return the federal campaign to its proper purpose.

It goes without saying that organizations devoted to changing public policy or testing it in courtrooms can provide valuable benefits to particular groups and to the larger society. The NAACP Legal Defense and Educational Fund, the Sierra Club, the Indian Law Resource Center and other groups that sued for access to the fund drive may, in the long view, do more for the well-being of people than the direct health and welfare service providers that, under the administration's plan, would be sole participants in the federal campaign.

But it is equally obvious that political advocacy groups, whose very purpose may be to ignite controversy, do not command the almost universal support that goes to more traditional charities. Such support is essential for the long-run success of a taxpayer-supported drive. Some advocacy groups may enjoy broad support. But who would be happy with a rule that allowed a federal agency to pick and choose among advocacy groups? It's worth remembering that when this issue first arose, during the Carter administration, much of the objection to including advocacy groups came from the political left, which opposed inclusion of anti-union organizations.

Of course, as the court noted, these groups have a First Amendment right to seek donations from federal workers and everyone else. But the combined campaign is not a public forum. It is a program using taxpayer-supported facilities and people. Like other government-supported programs, it can make sensible rules to serve a legitimate purpose. That purpose is to provide a convenient low- overhead way for federal workers to give to those voluntary agencies that help make life more tolerable for needy citizens in each community.

These are not high-profile agencies and, with declining federal support for community services, they are more hard-pressed than ever. Allowing groups serving more fashionable causes to compete for funds in combined campaigns may increase the total take. But much of that money might have been contributed through other channels anyway and some will come at the expense of traditional charities. That in itself is a good reason to keep the government's campaign fairly narrowly focused.