Mayor Bloomberg waded into a dicey free speech debate at Tufts University yesterday, telling graduating students that their school was right to allow debate on a controversial item in a conservative student journal.

During a commencement speech otherwise peppered with laugh lines, Mr. Bloomberg referred to a Christmas carol parody about affirmative action that appeared in the journal The Primary Source. He said he was glad the item was not suppressed despite the outrage of many who found it offensive.

“It was a classic example of free speech versus free speech,” Mr. Bloomberg said. “This country and other college campuses around the nation need more of that.”

The comment harked back to Mr. Bloomberg’s criticism of Columbia University last year. After student protesters derailed the appearance of a speaker from the conservative Minutemen Project, he said the school was not doing enough to protect free speech.

Mr. Bloomberg, who grew up about 10 miles from Tufts in Medford, Mass., spent most of his speech dispensing advice, telling students to take risks and work hard. He was also bestowed with an honorary doctorate from the school. He joked that his mother, who was in the audience, had always wanted him to become a doctor.

Mr. Bloomberg has been traveling the country delivering commencement speeches and taking on national policy issues. He will address students at the College of Staten Island and at Bard College later this week.