For several years now, more or less concurrent with the rising chorus of voices questioning the dearth of women in academic science generally and in the National Academy of Sciences in particular, the number and proportion of female scientists elected to the prestigious national honorary society has grown. Last year, 19 of the 72 full members chosen by the self-selecting group were women, a record.

Tuesday, the members of the NAS, which advises the federal government on science and technology issues, elected 72 people to join their ranks -- only 12 of whom were women, the lowest number and proportion in several years. The elections bring the total number of active members in the group to 2,013, of whom 199, or about 9.9 percent, are women. Despite the downturn this year, the overall proportion of members who are women is up from 7.7 percent in 2003.

A spokeswoman for the academy said that its officials were unavailable to comment because they were occupied with the group's annual meeting, at which the new members were elected.

But one prominent female scientist who has drawn significant attention to the issue of women in science, Nancy Hopkins of the Massachusetts Institute of Technology, said the proportion of women selected by the academy is not surprising, given the low proportions of women on science faculties -- and the fact that women are particularly underrepresented among the older and more established scientists who are likeliest to be elected to the prestigious academy.

Hopkins, who was voted in to the academy in 2004, noted a recent study she did for MIT's faculty newsletter that showed that the proportion of faculty members at the institute who are women had stagnated after a push prompted by a path breaking study she did on gender imbalance in 1999.

"People's expectations are a little bit out of line with reality, because they don't realize how few women there still are on these faculties" from which the National Academy of Sciences would be choosing, Hopkins said. It's not necessarily out of proportion for one of six new NAS members to be women, she said, when only 13 percent of the science faculty and under 14 percent of the engineering faculty at MIT today are women.

"If you want to increase the number of National Academy members," Hopkins said, "you have to get the number of female faculty members up."