One of every 12 books in the Fairfax County public library system disappears each year but the staff rarely knows the book is missing until someone tries to check it out.

The manual card and file system of borrowing books, used since the first public library was established in 1833, has become ineffective now that millions of books are borrowed annually in the Washington area.

In an effort to keep better track of books, Washington area library directors are installing and planning expensive new computerized circulation systems. They say these will help immediately determine who has a book, what books are overdue, who are delinquent borrowers and what books are on reserve. It will also help them send notices to library patrons who have overdue and reserve books.

Library officials said such an automatic system would immediately catch such borrowers as an Arlington woman who checked out 17 books and kept them six months. Library officials finally caught up with her two weeks ago, when another person asked to check out one of the books.

"The present system lacks circulation control," said William L. Whitesides, Fairfax County public library director.

Whitesides, like other area public library directors, said they are trying to get an automatic system like the one being used in the Martin Luther King Public Library in the District. Plans are to install similar systems in all branches in D.C., according to library officials.

"It's doing beautifully," D.C. director Hardy Franklin, said of the $180,000 Martin Luther King Library system.

Franklin said the system has made it easier not only to retrieve overdue books, but to keep abreast of what library users are reading.

Arlington County is in the process of installing an automatic circulation system and library officials in Montgomery and Prince George's counties said they are planning for one but doubt they will get it next year because of the lack of money.

An Alexandria library official said the city has no immediate plans to place an automatic system in its libraries.

Whitesides and the Fairfax County library board recently aksed the county Board of Supervisors to consider spending $400,000 to $450,000 for an automatic circulation system. The supervisors have not made a decision.

Whitesides estimates the county loses about 80,000 (not including outright theft) of its 1.2 million books each year because of library staf "can't retrieve the overdue books from the borrowers."

"Ninety-nine per cent of the patrons tend to return books, but there are some who forget an need to be reminded," Whitesides said.

He said the present massive card file circulation system makes it difficult for the library staff to notify delinquent borrowers for weeks and months.

Whitesides said an additional 20,000 books are stolen from library shelves each year.

He said the book loss costs about $800,000 annually.

In Arlington, 4,000 books are lost annually from the 100,000 in circulation, according to Lelia B. Saunders, assistant county public library director.

"We've never been able to take an accurate inventory," Saunders said.

However, she said the new automatic system that is being installed should help determine how many books are in the system.

Library officials in Montgomery and Prince George's counties and the District said they have no estimate of how many books disappear each year.

"We don't have any definite figure" (of lost of books), said Franklin, the D.C. official. "That's one of the reasons why we wanted to go to the computerized system."