Gloria Steinem and Pat Carbine of Ms. Magazine last night officially deposited the magazine's ten-year collection of letters-to-the-editor in the Schlesinger Library, marking the first time the library has included a magazine's letters in its collection.

President Horner said she was "absolutely thrilled" the library had received the letters, because "there is no better way to understand social history in an era of rapid change than to read letters like these."

Since its start in 1972, Ms. Magazine has received an overwhelming response from its readers, Pat Carbine, publisher and editor-in-chief of the magazine, said yesterday, nothing that over 20,000 readers responded to the first issue alone. The first letter published--which Carbine read aloud at the press conference--was a response to an article by Horner entitled "Why I Fear Success," she added.

The Schlesinger Library--which has one of the finest collections of materials on women's history in America--has received seven cartons of letters and will soon receive several more.

To guard the privacy of their authors, letters will not be available to researchers until they are ten years old, Eva Mosley, curator of manuscripts at the library said yesterday. Mosley added that an exception has been made in the case of letters about the Equal Rights Amendment, because of the immediacy of the issue. Anyone wanting to use the letters will be required to sign a statement promising not to use the names of letter-writers.

Personal Histories

Gloria Steinem, editor of the magazine and one of its founders, said the letters were special because many of them are expressions of women's personal lives. "What diaries were to the 19th century, these letters are to the 20th," she said.

Steinem said the letters chronicled the development of the women's movement. In the early letters women describe problems they faced as a result of chauvinist discrimination. she said, adding that more recent letters ask the question. "Now more than ever--what can we do about Ronald Reagan?"

After the press conference Sullivan, editor of "Fine Lines", an anthology of women's fiction that appeared in Ms., led a discussion between women writers and literary critics on whether there is a uniquely feminine style of writing.