Brain surgeons do it. Lawyers do it. Even Elks do it. But music librarians haven't done it in the United States since 1968. Last year, they did it in Belgium, and earlier years have seen them doing it in Hungary, England and Austria.

Today, however, the International Convention of Music Librarians returns to the United States when it opens in Rosslyn. "What we have tried to do as the hosts is to show our colleagues from abroad the diversity of American music and how we run our libraries," said Neil Ratliff, head of the music library at the University of Maryland and chairman of the convention. There are, according to Ratliff, 60 or 70 music librarians in the metropolitan area.

Ratliff says the convention will, among other things, deal with "typical problems" music librarians find in their work. "Just the physical handling of phonograph records--deterioration--do you put them on tape for users so they don't wear out? And if you do, then you have to worry about copyrights."

The convention, which runs through this Saturday, is sponsored by the International Association of Music Libraries and the International Association of Sound Archives. Through Thursday a variety of lectures, workshops and concerts in styles ranging from jazz to the classical avant-garde will take place at the West Park Hotel in Rosslyn. On Friday the convention moves to the Library of Congress.

As of last Wednesday 283 people had registered, primarily music librarians and heads of national music centers. There are also some librarians from broadcast libraries, such as those of the BBC and the German national radio. Ratliff describes a music librarian as one who deals with all the resources of the music world: "sheet music, scores, books about music, sound recordings."