CHICAGO — As his name was tossed back and forth yesterday in the fury of the presidential campaign, 1960s radical William Ayers spent the day as he often does, working quietly as a professor and trying to ignore the political tempest.

Officials at the University of Illinois-Chicago say Ayers is on a "previously scheduled" sabbatical, but he was on campus yesterday, sitting on a lunch-hour doctoral dissertation panel.

The man who was a Weather Underground member and decades later had dealings with Barack Obama is being increasingly cited by John McCain's supporters, who accuse Obama of "palling around with terrorists." Obama's campaign counters that McCain is using "smears" involving Ayers to distract voters from the economic crisis.

When the Chicago Tribune caught up with Ayers yesterday, he declined to join the unpleasant conversation.

"What could I possibly add?" he asked. "Life happens."

Earlier in this campaign, Obama's controversial former pastor, the Rev. Jeremiah Wright Jr., only heightened attention on his past remarks by defending them. Ayers has avoided public statements, and indeed declined further comment with the Tribune.

McCain told a St. Louis radio station yesterday that he is likely to bring up Ayers at today's debate. The Obama campaign unveiled a radio ad declaring, "When Ayers committed crimes in the '60s, Obama was 8 years old. Obama condemned those despicable acts. Ayers has had no role in Obama's campaign, and will have no role in his administration."

Ayers was an anti-war activist in the late 1960s and early 1970s, and joined the Weathermen, which later became the Weather Underground. The group set off bombs at government buildings.

When Obama began his first state Senate bid in the mid-'90s, he visited Ayers' home for a meeting. Ayers and Obama also worked together on school reform issues. The McCain camp issued a statement yesterday that Obama had "made an independent judgment to befriend an unrepentant terrorist."

The blistering criticism of Ayers comes as a shock to colleagues at the university, where he's seen as "a really nice guy," said Phillip Kisunzu, a research assistant who works across the hall from Ayers. Kisunzu said he asked Ayers about the furor.

"I brought it up because I hear his name on the news," Kisunzu said. "I heard it again today."

On Ayers' office door, along with pictures of Che Guevara and Malcolm X, is a cartoon of a man interviewing for a job. The interviewer says, "I'm trying to find a way to balance your strengths against your felonies."

Ayers rarely mentions presidential politics, said colleague Bill Schubert, who defended Ayers in a letter to The Chronicle of Higher Education over the weekend and sat with him on the dissertation committee yesterday. Graduate student Isabel Nunez successfully defended her dissertation posing that educators should learn from school and outside life alike.

Ayers' advice to her, Schubert said, was "You don't always have to have an ultimate answer to the toughest questions."