'Primer' aids the novice in choosing, buying and maintaining oriental rugs; ORIENTAL RUG PRIMER: Buying and Understanding New Oriental Rugs, by Aram Jerrehian. New York: Facts on File. $12.95.

For the novice who has just come to appreciate oriental rugs, purchasing one can seem like a bewildering ordeal. Aram Jerrehian's book intends to present the first-time buyer with facts about orientals in a clear and practical format.

Covering only new rugs, the "Primer" deals in a methodical way with their construction, basic styles, and maintenance.Mr. Jerrehian includes chapters on where to buy and how to select a carpet as well as an interesting chapter on buying for investment purposes. There is a useful directory of major rug types, a glossary of terms, and 32 pages of good color photographs.

Mr. Jerrehian's practical approach to his subject meets a definite need. It will certainly help readers make their first purchase with greater confidence. Nevertheless, the book is disappointing in several ways.

Mr. Jerrehian skips over the centuries- long history of rug-making in a scant six pages. The novice learning to appreciate new rugs will gain little knowledge from this book about the fascinating traditions which produce them.

"Oriental Rug Primer" is, for the most part, clearly written. But its prose is totally devoid of the elements which make entertaining and memorable reading. Simplicity and practicalilty needn't preclude humor and charm.

The book is also poorly organized. The reader doesn't get to the interesting subject of color, design, and selection until he has been forced to slog through a boring chapter on the technical aspects of weaving and a confusing discussion of where to buy. Reversing the order of topics might have made a more agreeable presentation.

Finally, the color plates are illogically lumped together in an early chapter on weaving. It would have made more sense to bind the photographs adjacent to a later chapter describing rug types. The same is true of the black-and-white drawings of design elements which adorn the first page of each chapter. The drawings are never where you want them -- in the text where they are actually discussed.

Despite its shortcomings, however, "ORiental Rug Primer" is an inexpensive guide the rug-buying novice will find useful and informative, if not entertaining, reading.