Approximately 2900 students will be officially enrolled in the 1957 Harvard University Summer School by five o'clock tomorrow night, according to preregistration estimates released yesterday by Suzanne M. Hildebrand, Executive Secretary of the Summer School Office.

The summer session will be officially opened at a Convocation Reception in Sanders Theatre tomorrow at 8 p.m. William Yandell Elliot, Director of the Summer School and Leroy B. Williams Professor of History and Political Sciences, will deliver welcoming remarks. He will introduce McGeorge Bundy, Dean of the Faculty of Arts and Sciences, who will speak.

Immediately following the Reception, a Convocation dance will begin in Memorial Hall, with music provided by George Graham's orchestra until midnight, according to Social Director, Joan E. Hartman. This dance will be open without charge to Summer School students, faculty, and their guests, Miss Hartman said.

The 1957 enrollment figure will represent an increase of nearly ten percent, Miss Hildebrand revealed. The enrollment last year was 2686. Enrollment figures have risen steadily, she noted, since the end of the World War II veterans boom caused a slump in 1953.

The male-female dis tribution, however, has apparently reached a balance in the last three, she said, with roughly 60 percent male and 40 percent female students. These figures represent a sharp upsurge of female attendance over earlier sessions.

Geographic distribution will again be extremely broad, according to Miss Hildebrand, with 45-48 states, plus the District of Columbia and nearly all Territories represented.

The steady increase in Summer School enrollment has rendered the dormitory space within the Yard insufficient, Miss Hildebrand admitted, but noted that Graduate School dormitories have thus far succeeded in absorbing the overflow. This year, for the first time, Will James Hall will be completely filled.

Although small waiting lists do form before registration, she noted that last-minute withdrawals generally take care of them. Rooms not claimed before 2 p.m. tomorrow will be reassigned, she warned, unless specific notice has been given of late arrival.