The Office of Personnel Management has issued its final rules for the Combined Federal Campaign, the government's annual charity drive, which agency officials say will probably exclude 18 non-profit groups that have participated in the past.

The new rules exclude groups that do not provide direct health and welfare services, such as the National Right-to-Work Legal Defense Fund, the Audubon Society and the National Organization for Women's Legal and Education Defense Fund.

The OPM has argued that the advocacy groups are the reason why participation in the campaign dropped 1 percent from 1981 to 1982.

But the advocacy groups say the rules are part of the Reagan administration's attempts to restrict their efforts.

The rules had eliminated 25 groups, but a federal judge has ordered the OPM to reinstate seven groups. The OPM told the court it will consider admitting groups that are "similarly situated."

The reinstated groups include the NAACP Legal Defense and Education Fund Inc., the Sierra Club Legal Defense Fund and the Federally Employed Women Legal Defense Fund.

"Recently," OPM spokesman Patrick Korten said, "the National Socialist White People's Party asked to join. Where will it end if we can't control access?"