Mather House Co-Masters David J. and Patricia A. Herlihy, best known among students for their efforts to ease house overcrowding and make the partially completed structure more livable, will leave Harvard at the end of the spring semester to accept twin lifetime positions at Brown.

The Herlihys, who have overseen Mather House activities for 10 years, said that they accepted the two offers--his in medieval history and hers in Russian history--so that Patricia Herlihy could pursue her scholarly career in a tenured position.

The move will involve the unusual resignation of David Herlihy from an endowed lifetime post as Harvard's Lea Professor of Medieval History.

The Herlihys' departure will also mark the second time within as many months that house masters have said they will leave the traditionally five year job, which requires faculty members or administrators to oversee house policy and serve as nonacademic liaisons between undergraduates and the dean of the College.

In December, Currier House Masters Dudley R. and Georgene B. Herschbach announced their decision to resign their co-mastership at the end of the spring term. The Herschbachs will remain at Harvard.

College officials yesterday said the search for new Mather masters is not yet underway.

Happy Days

The Herlihys' announcement came in a January 26 letter to Mather House residents in which the masters called their years in the house "among the happiest of our lives."

"Brown University has offered us both tenured appointments in its Department of History. As you probably realize, it is extremely difficult for a husband and wife to obtaintenured posts in the same department," the letterreads.

David Herlihy, who teaches the popular CoreCurriculum course, Historical Study B-15. "TheBlack Death," said yesterday that the joint postsarose through lucky coincidence. A seniormedievalist at Brown retired, and a Russianhistorian decided to take on more administrativeresponsibilities, creating openings in theHerlihys' special fields, he said.

"For Pat in particular," the Herlihys' lettercontinues, "it is an exceptional opportunity toreturn under excellent terms to fulltime teachingand research in Russian history."

Patricia Herlihy taught at Brown for two yearsas a visiting professor. She has also taught on atemporary basis at Wellesley College, theUniversity of Rhode Island and BrandeisUniversity, and has been an instructor in Russianand Soviet History at Harvard's Extension School.

"I'm usually substituting for other people onleave," she said yesterday. "I was hoping for abreak somewhere."

Job security was the primary factor in theHerlihys' decision to leave Harvard, PatriciaHerlihy said. Faculty members without tenure arenot guaranteed teaching positions on a long-termbasis.

Patricia Herlihy added that she had "beenlooking in the vicinity ever since we arrived" fora permanent teaching job, preferably one to whichshe could commute. "If I could have taughtanywhere within a reasonable radius I would havestayed," she said. "I hate leaving Mather House. Iloved it here."