Prince George's County Libraries have begun using an automated system for keeping track of books, records and other materials atthe Oxon Hill Branch, the first of 20 Prince George's branch libraries to be converted to computerized recordkeeping.

The $450,000 system, to be installed over a three-year period at all county libraries, was designed to expedite services for patrons, streamline clerical work and help conserve library collections.

Bar coding similar to that used in department and grocery stores will identify books and other materials, so that search and filing time will be cut dramatically.

"With automated circulation, patrons will be able to find out quickly whether an item is on the shelf or in circulation, and reserving a book will be a much simpler and faster process," said library administrator Judy Cooper. "And we will be able to keep closer tabs on overdue materials."

The computer also will print library cards, overdue notices and statistical reports -- all previously done manually by staff personnel. According to library officials, the average cost of a book has risen from $5.83 to $11.06 in four years, and the computerized system will also save money by reducing the number of titles that have to be replaced.

After the system was unveiled at a recent opening ceremony, Oxon Hill patrons could look over the three new terminals and watch library staffers scan books and borrowers' cards, linking the two codes for storage in the computer. Some tried to peer around the desk to get a closer look at the screen. Others seemed suspicious of the new technology.

"One thing people seem to fear about computerized circulation is that it will mean an invasion of their privacy," Cooper said. "They want to know who has access to the records of the books they check out. In fact, library personnel don't know what someone has checked out unless an item becomes ovedue. When the book is returned, the record is erased. The confidentiality of circulation records is protected by law. We can't release that information to law officials or anyone else."

Library officials said there may be some delays at first, until library staff members become accustomed to the equipment and the coding of books is completed. Following Oxon Hill, the largest and busiest county libraries are scheduled to go "on line" next. The New Carrollton and Bowie branches are to be converted in November, and Hyattsville is scheduled to make the switch next January. The remaining 17 branches will adopt the system gradually over the next two years. C.L. Systems Inc. is installing the equipment, under a contract awarded by the library in 1979.

The library systems of Montgomery County and the District, which have collections comparable in size to Prince George's, already have computerized circulation at all branches. In Virginia, Fairfax County is phasing in automation and expects to have all branches converted by 1984. Because of differences in the four record-keeping systems, however, a library card will be usable only in the jurisdiction where it was issued.