Ralph Nader, whose one-man crusade against corporate shenanigans became a multimillion-dollar center for consumer activism, yesterday resigned as head of Public Citizen Inc., the umbrella group that is the center of his lobbying ventures.

Nader turned over the day-to-day operation of Public Citizen to Dr. Sidney Wolfe, head of the Health Research Group, another Nader-sponsored organization. Wolfe will continue to run the health activist organization.

In an interview, Nader said the move is designed to free him from managerial responsibilities so he can spend time building an endowment for Public Citizen as it approaches its 10th anniversary and other national and international activities.

Nader, 46, will continue to run the Center for the Study of Responsive Law and a variety of other groups dealing with issues ranging from insurance to broadcasting. He also will continue to stay in regular contact with Public Citizen workers. Public Citizen includes health, antinuclear, lobbying and litigation units.

The resignation comes at a time when Nader's Congress Watch organization, a branch of Public Citizen, is without a permanent leader, in light of the fact that long-time Nader aide Mark Green is running for Congress in New York City. Congress Watch, the Nader legislative lobbying arm, is being run by an acting director, Nancy Drabble.

In addition to the fundraising work, Nader said he is "very interested in seeing more coordination between consumer groups in other countries and this country." Further, he said he wants to spend more time on setting up local and national activist groups on emerging issues such as banking.

"The 10th anniversary is a good time for taking stock and building an endowment," he said. "We want to develop instruments for consumer organizations," he added, pointing to programs such as one to solicit consumer views and money with cards enclosed with utility bills.

Essentially, the proliferation of the Nader organizations has forced him to spend considerable time handling the administrative duties that accompany the operation of any large organization.

Wolfe said the change at the top of Public Citizen would mean little to the organization's direction. "I have been, for the last year or two, gradually assuming a certain number of responsibilities of overseeing Public Citizen in terms of fundraising activities and interviewing everyone who gets hired," Wolfe said. "Now I'm just taking over the reins totally."