OBERLIN, Ohio — Oberlin College, known as much for ardent liberalism as for academic excellence, canceled classes on Monday and convened a “day of solidarity” after the latest in a monthlong string of what it called hate-related incidents and vandalism.

At an emotional gathering in the packed 1,200-seat campus chapel, the college president, Marvin Krislov, apologized on behalf of the college to students who felt threatened by the incidents and said classes were canceled for “a different type of educational exercise,” one intended to hold “an honest discussion, even a difficult discussion.”

In the last month, racist, anti-Semitic and antigay messages have been left around campus, a jarring incongruity in a place with the liberal political leanings and traditions of Oberlin, a school of 2,800 students in Ohio, about 30 miles southwest of Cleveland. Guides to colleges routinely list it as among the most progressive, activist and gay-friendly schools in the country.

The incidents included slurs written on Black History Month posters, drawings of swastikas and the message “Whites Only” scrawled above a water fountain. After midnight on Sunday, someone reported seeing a person dressed in a white robe and hood near the Afrikan Heritage House. Mr. Krislov and three deans announced the sighting in a community-wide e-mail early Monday morning.