Henry Moses, who died yesterday at 66, was headmaster of Trinity School, the elite preparatory school on West 91st Street where Latin and Greek still form an integral part of the curriculum. He died of complications following a heart transplant, the school announced. A veteran college administrator who served as dean of freshman at Harvard, Moses was an expert on the transition to college. He wrote a guidebook for students, “Inside College: New Freedom, New Responsibility” (1990).

At Trinity, he oversaw the construction of a 43,000-square-foot middle school building that included two floors of classrooms and an underground gym that opened in 1999. The building attempted to preserve what Moses called the “school-ness” of Trinity — including the installation of an ancient parish-house bell that had been part of an earlier structure on the site.

Trinity administrators credit Moses with raising the school’s reputation.

“Hank Moses was a true visionary and a tireless leader for Trinity,” the president of the Board of Trustees, Andrew Brownstein, said. “Every member of this community feels his loss.”

Moses was born August 18, 1941, in Washington, D.C. A 1963 graduate of Princeton University, Moses earned a Ph.D. in English from Cornell University in 1968 and worked in the dean’s offices at Cornell, Princeton, and the University of Virginia. In 1973, he became dean of students at Manhattanville College and also taught courses in the English Department. At Harvard, where Moses became dean of freshman in 1977, he introduced the First-Year Outdoor Program, a summer program resembling Outward Bound for incoming freshmen. He also was a lecturer in American literature and taught upper-level courses on William Faulkner.

“Hank was a superb Harvard colleague: wise, funny, respectful of tradition but able to think out of the box, courageous, and kind,” recalled the current dean of freshmen at Harvard College, Tom Dingman. “His analytical ability was sharp as was his capacity to understand and relate to students and faculty.”

While still a Harvard dean, Moses began running college orientation retreats for Trinity seniors, and in 1991 he became the school’s 27th headmaster. As head of one of the oldest schools in America — Trinity was founded in 1709 as an adjunct to Trinity Church on Wall Street — he was conspicuously conscious of his role in fostering a traditional liberal education. “At its best, liberal education is education in skepticism — I mean the ‘yes … but’ argument,” he wrote in a recent Trinity publication. “Students at Trinity learn to hold two or more mutually challenging ideas in their mind at the same time.” Many also hold in their minds classical verse; the school is noted for its Virgil Academy, in which seniors are grilled by a panel of classics scholars on the minutiae of the Aeneid.

Moses also oversaw the creation of a historical archive in preparation for Trinity’s tercentennial next year. Trinity’s endowment grew to $51 million in 2007, from $6 million when he arrived.

At Trinity, he would walk through the halls greeting students, teachers, and parents, occasionally challenging them to impromptu arm wrestling matches. A dedicated outdoorsman, he enjoyed running, cycling, backpacking, and mountain climbing. Visitors to his office at Trinity were often greeted by the sight of his mountain bike, which was usually covered in mud.

Surviving him are his wife, Mary Sarah Holland; his children, James, Bruce, Paige, Laurence, and William; four grandchildren, and his father, Henry Moses.