Boston ? Lawrence Summers’ bluntness has earned him both enemies and admirers in several top Treasury Department jobs and now as president of Harvard.

He’s rarely been one to apologize for his directness — until this week. Summers has spent much of the last few days saying sorry after a tumult over comments he made at a conference on women in science that he thought were off the record.

Summers insists his remarks about possible biological differences in scientific ability between men and women have been misrepresented — that he wasn’t endorsing a position, just stating there is research that suggests such a difference may exist. But his words have sparked wide discussion on Harvard’s campus and a string of angry calls and e-mails.

In a letter to the Harvard community posted late Wednesday on the university Web site, Summers wrote: “I deeply regret the impact of my comments and apologize for not having weighed them more carefully.”

“I was wrong to have spoken in a way that was an unintended signal of discouragement to talented girls and women,” he added in what was his third statement expressing contrition since the Jan. 14 conference.

Summers, an economist by training, said in a telephone interview that he hoped he would be able to participate in academic discussions in the future.

“But particularly on sensitive topics, I will speak in much less spontaneous ways and in ways that are much more mindful of my position as president,” he said.

Some academics think that’s too bad. They say it’s important for college presidents to be engaged in debating important issues, and worry this episode will discourage them.

“It’s rare that a university president comes and offers provocative ideas,” said Richard Freeman, an economist at Harvard and the National Bureau of Economic Research, the Cambridge research institute that hosted the conference where Summers spoke.

Freeman and several other participants at the conference say Summers has been portrayed unfairly. They say he was simply outlining possible reasons why women aren’t filling as many top science jobs as men.