At the Walden book store at Montgomery Mall yesterday, J. R. Tolkien's "The Silmarillion" was being sold at $10.95 a copy, the list price.

The Discount Book Shop at 5454 Wisconsin Ave., in Chevy Chase, was offering the best-seller at a discount of 20 per cent, or $8.76.

Sidney Kramer's book store at 336 Pennyslvaina Ave. SE was sold out of the Tolkien work and a salesperson said new copies are expected in two weeks. Kramer had been selling the book, No 1 on The New York Times list of best-sellers, at a discount of 15 per cent.

Out on Rockville Pike, however, there were plenty of copies of the book and the price was $7.12 - a steep discount of 35 per cent.

The site in Montgomery County is the location of a new venture into discount book selling by Dart Drug Corp., called Crown Books. Since the new store opened Sept. 24, "business has been tremendous," said 24-year- old Robert Haft, head of the book store operation and son of Dart founder and president Herbert H. Haft.

Crown is located in a 3,000-square-foot store at 12111 Rockville Pike, across from a Memco store. Dart Drug, the area's third-largest retail drug drain, is planning to add several additional Crown book stores in the metropolitan area in future months. More expansion is possible next year with a reported goal of 10 units in a year.

The prototype book store, which Haft said carries 10,000 separate titles out of some 200,000 books in print, is open seven days a week (until midnight every day but Sunday). Discounts are offered on all books and on magazines as well - an unusual development in the retailing of publications.

Fortune magazine, with a list price of $2 a copy, is selling for $1.80 at Crown; Washingtonian magazine, listing for $1.50, is being sold at $1.35.

Haft said his store will offer 35 per cent discounts on all hard cover books listed by The New York Times as a best-seller. Discounts yesterday ranged from 20 per cent to 50 per cent and Haft said his policy will be to discount paperback books by 25 per cent.

A visitor to the store yesterday noted that hardbacks are grouped by subject with sections of hardbacks and paperbacks divided by general price ranges. Industry sources said the operation was unusual in extending discounts to mass-market paperbacks and Haft said he thinks the new store's price policy is being matched by only a handful of shops around the country.

Haft, a graduate of the Harvard University Graduate Scholl of Business, said that when he returned to the Washington area from Cambridge, Mass., he was "disturbed" to see so many books being sold at list prices. Citing examples of widespread discounting in such cities as Kansas City, Los Angelees, New York and Boston. Haft said he saw a business opportunity here.

In and interview, Haft said the 35 per cent discount for hardback best-sellers is "at cost or below" in most instances. Thus, these books are being used as merchandise promotion to attract customers, in the hope they will buy other books or magazines - which are discounted less.

Dart's expansion into spearate bookstores is the latest in a series of retail diversifications by area companies Drug Fair Inc., for example, recently launched a series of jeans stores called Wrangler Wranches, featuring Wrangler brand lines. Giant Food Inc. owns pharmacies and the Pants Corrals, which feature Levi Strauss products.