The Wellesley College board of trustees has selected a Harvard professor to be the school's next president, Wellesley officials announced yesterday.

Diane Chapman Walsh, professor and chair of the department of health and social behavior at the Harvard School of Public Health, was chosen to succeed Nannerl O. Keohane, who left to assume the presidency of Duke University earlier this year.

Walsh, a Wellesley graduate, will assume the post October 1. She was chosen following a six-month search by a committee including faculty, staff, students and trustees.

Walsh has done work in the areas of work site drinking, social marketing for public health and disease prevention, Wellesley officials said.

"Being selected as Wellesley's 12th president is a great honor," Walsh said in a statement released yesterday. "I approach this new challenge with excitement and humility, and in the sure knowledge that I will have much support from the thousands of extraordinary women and men who care deeply about the future of Wellesley and the future of the world."

Gail H. Klapper, chair of the presidential search board, said Walsh is "a distinguished researcher and gifted teacher who brings a striking constellation of talents to Wellesley."

"Her outstanding career in the promotion of health and the prevention of illness, combined with her commitment to the liberal arts and the higher education of women, will lead the college in new and exciting directions," Klapper said.

Keohane, who is married to Stan-field Professor of International Peace Robert O. Keohane, was awarded an honorary degree at Harvard's Commencement Exercises in June.