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. Mr. Summers has spent much of the last few days saying sorry following a tumult over comments he made at a conference on women in science that he thought were off the record.

Mr. 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, Mr. 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 conference last Friday.

Mr. Summers, an economist by training, said in a telephone interview that he hopes he’ll 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 Mr. Summers spoke. “All too often in universities somebody comes and it’s like cutting a ribbon, and they mouth some platitudes.”

Mr. Summers already had a reputation as brilliant but indelicate, and drew attention in 2002 when a prominent black studies professor, Cornel West, left Harvard after a dispute with Mr. Summers.

But Mr. Freeman and several other participants at last Friday’s conference say Mr. 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.

“He didn’t say anything that people in that room didn’t have in their own minds,” said Claudia Goldin, another Harvard and NBER economist who attended the conference. Ms. Goldin said Mr. Summers simply summarized research from papers presented at the conference. “Why can they say them and he can’t?”

The short answer – because Mr. Summers is president of Harvard. Mr. Summers acknowledged the rules are different for him, and critics say Mr. Summers’s influential position is precisely why they were so offended.

“We need to be drawing on all of the talent of our population,” said University of Washington engineering school dean Denise Denton, who confronted Mr. Summers about his comments in a telephone interview. “The notion that half the population may not be up to the task, even remotely getting that idea out there, especially from the leader of a major university in the United States, that’s of concern.”

Women comprise a majority of undergraduates in all subjects nationwide, but have lagged in ascending to top university science jobs. The debate over why this is so was renewed at Harvard this year after only a few female scientists were put forward for tenure. Mr. Summers said bringing more women into the sciences is a top priority.

But MIT biologist Nancy Hopkins, who walked out of Mr. Summers’s talk and said it made her “nauseous,” said the president was expressing his own views at the conference – and setting an unacceptable tone for Harvard.

Mr. Summers reiterated to the AP that he “was not expressing convictions” but avoided apologizing for raising the issue at all. “I certainly believe that every subject should be brought to bear in research on vitally important problems,” he said.

As Treasury secretary under President Clinton, Mr. Summers held the power to move markets with an offhand comment, and was accustomed to having every utterance scrutinized. But in this case, he believed the conference proceedings would remain private. An account was of the meeting was first published in The Boston Globe.