Arlington librarians are putting their brand on some of the county's rare books in an effort to deter theft.

A number of old books in the county library system's Virginiana collection have illustrations that thieves recently have found desirable, and so the system has begun to emboss those plates with an Arlington County Public Library seal.

"These are books which are valuable only for their contents," said Lelia Saunders, director of the 500,000-volume Arlington system. "There is no real reason for us to preserve them in their original condition . To the library, they are useful to people because of the information in the book itself, not because of the plates."

In the last six weeks, library staff members have found a number of mutilated books from which prints were removed. Two books were separated from their covers and taken from the library, with the covers left behind. Several others had the pages on which plates appear ripped out. One 13-volume set of books had more than 200 pages torn out.

Saunders said she suspects prints are being taken "because they can sell them. My feeling is that this is being done by somebody who can see a market for them."

Embossing volumes with the identification of the owning library is a relatively common, though regrettable, practice, according to rare book librarians. The Library of Congress embosses its rare books and manuscripts to discourage their theft.

"These are very sensitive issues," said William Matheson, chief of the Library of Congress' rare book and special collections division. "One tries to avoid defacing the book while trying to protect it."

Marking is done, Matheson said, "in response to the recognition that if something is stolen and has no mark, how will the institution ever be able to demonstrate that it was ever in its collection?"

The books pillaged at Arlington's libraries come from a collection of works about Virginia. Some of the books are unusual, according to Saunders, and some date back to the 19th century, but none is considered "rare" in the technical sense that scholars use to refer to extraordinarily valuable books and manuscripts.

The books do not circulate and, according to Saunders, those considered most precious by the staff have been locked up. "If we had space, we'd lock them all up," Saunders said. The library also has bought two security mirrors to make the areas where the books are often used more visible to library staff.

Kenneth Carpenter, chairman of the preservation committee of Harvard University's library system, acknowledged that embossing "is done in a lot of places. I really do hate the idea, but it does seem to be something people are doing to protect their collections."