Facing mounting pressure on campus and in the national press, University President Lawrence H. Summers issued last night his most extensive apology since suggesting on Friday that “innate differences” between the sexes may account in part for the underrepresentation of women on elite science faculties.

“I deeply regret the impact of my comments and apologize for not having weighed them more carefully,” Summers wrote in an open letter to the Harvard community.

“I was wrong to have spoken in a way that has resulted in an unintended signal of discouragement to talented girls and women,” he added in the six-paragraph statement posted on his website. “As a university president, I consider nothing more important than helping to create an environment, at Harvard and beyond, in which every one of us can pursue our intellectual passions and realize our aspirations to the fullest possible extent.”

The apology came after a three-day media frenzy and a barrage of criticism from academics at Harvard and across the nation.

Immediate reaction to the apology was mixed. Student leaders of campus women’s groups praised the president’s statement, but two members of the Faculty Standing Committee on Women said the letter would not heal the wounds still stinging from Summers’ remarks last week at a National Bureau of Economic Research symposium.

The letter “puts a huge smile on my face,” said Connie Zong ’05, co-vice president of Women in Science at Harvard Radcliffe.

But Summers’ statement failed to assuage anger among Standing Committee members, who yesterday sent a letter to the president blasting him for sending “at best mixed signals to our high-achieving women students.”

“I fear it’s going to take much more than a letter to repair the damage that’s been done,” said Kay K. Shelemay, the Watts professor of music.

Professor of Economics Caroline M. Hoxby ’88 said the letter “doesn’t really change the environment for graduate students who feel their ability has been questioned and for undergraduates who are taking exams.” She said the Standing Committee planned to meet this morning.

Melissa E.B. Franklin, the Mallinckrodt professor of physics, who has been one of the president’s most vehement critics this week, called Summers’ letter “a great step forward.”

“There are probably quite a few members of the Harvard faculty who actually believe that there is an innate difference between girls and boys in science skill,” Franklin said. “Now that this is brought up, maybe all the ensuing discussion will be able to convince those people otherwise.”

Nancy Hopkins '64, the MIT biologist who first objected to Summers' remarks and reported them to the media, said today she was nonplussed by the president's apology.

"One still has to be deeply concerned about what he said on Friday. Unfortunately, there really isn't yet any convincing evidence that he was misunderstood," Hopkins said.

As students hunkered down for the final stretch of exams, word of Summers’ letter moved slowly across campus.

The two co-chairs of the Radcliffe Union of Students, Dara F. Goodman ’07 and Giselle B. Schuetz ’07, both said they hoped Summers would follow up his words with concrete actions to bolster the position of female scientists at Harvard.