Toiling for years as a Democratic operative and senior appointee to President Clinton, Mark D. Gearan always nurtured a quiet ambition: He wanted to be a college president.

Yesterday, Gearan announced that his dream is coming to pass. He will step down as director of the Peace Corps to take the helm of Hobart & William Smith Colleges in Upstate New York.

Aspiring to the groves of academe is a somewhat unconventional ambition by the standards of the political world, especially for someone like Gearan, who does not have a doctorate. And finding a president in the corridors of Washington is a somewhat unconventional choice for the small liberal arts institution.

But Gearan, 42, said yesterday he thinks there are some marked similarities between the old job and new.

Both the Peace Corps and the college "are mission-oriented and values-centered" institutions, he said, and both have an international outlook. Some 62 percent of Hobart & William Smith students study abroad for part of the time they are pursuing degrees.

Gearan, who served as deputy chief of staff as well as communications director to Clinton during his first term before being appointed Peace Corps director four years ago, announced his departure to staff at Peace Corps headquarters at 20th and L streets NW yesterday afternoon. He spoke by phone with Clinton, whom he first got to know while serving as director of the Democratic Governors Association from 1989 to 1992, and Gore, for whom he served as campaign manager in the 1992 campaign.

Amid the turbulence of Clinton's first term, in which the administration's relations with the news media and Congress were erratic at best, the good-humored Gearan was a respected figure within the White House and outside. Possessed of a whimsical streak, Gearan often walked around the campaign trail or the White House with his video camera rolling; it was a way of compensating for the amount of time the job forced him to be away from home. A for-hire pianist in his younger days, he is sometimes pressed into service at Washington parties.

Gearan will move to the Hobart & William Smith campus, in the waterfront town of Geneva in New York's scenic Finger Lakes region, at the end of the summer.

In his tenure at the Peace Corps, Gearan traveled to more than 30 countries (including Mongolia, where proud authorities gave him a lesson in how to prepare the rodent they were serving him for dinner). The service agency, started under President John F. Kennedy, has found a somewhat more secure footing under Gearan's watch. Last week, Congress for the first time gave the agency a four-year (as opposed to annual) authorization, and put the Peace Corps on a track to increase to 10,000 volunteers (from its current 6,700). If achieved, this would be the highest number of Peace Corps volunteers since the 1960s.

CAPTION: Mark D. Gearan expanded Peace Corps into several countries.