They're not bestsellers. They're probably not even on class reading lists. But for students searching for the perfect cure for overwork and exhaustion on a Friday afternoon, the Harvard Library System's monthly booksale of discards might be the answer.

Boasting titles including Elizabethan Drama and Its Mad Folk, Revolution in Poetic Language and the World Almanac of 1974, the Widener Library tradition is perfect for book lovers.

"It's interesting to wonder who read it, under what circumstances, and whether it was part of a family fortune," said Anne Merrill, a Widener clerk. Merrill, running the cash box at the Widener basement sale, pointed to a copy of Histoire des Ordres Religieux, a rare collection at the sale priced at $100.

The French history was one of about 500 books selected from the University's 11 million volumes for sale yesterday, chosen because, for one reason or another, Harvard's 100 libraries no longer want them for their collections.

The Histoire is a seven-volume collection printed during the French Revolution on well-preserved, ragbased paper that makes a crinkling sound when touched.

Members of the University library system's gifts and exchange department spend each month selecting, pricing and arranging the books, said Jean-Philippe Wheeler, department head. Prices range from 10 cents to $ 100, he said.

Fixing Prices

Each month's proceeds, $300 to $900, goes toward purchasing more books for Harvard libraries.

"The process of deciding which books will be part of the sale is very complicated," said Wheeler, speaking in a faint accent from his native France. Widener alone employs 10 collection reviewers.

At times, the director said, some-what rare books may require hours of cross referencing to determine a price. Wheeler, employed at Harvard for 15 years, said that only a true "book person" could fill his job, which he said requires subtle and somewhat obscure knowledge.

The director, never trained to work with books, makes daily judgments based on arcane facts, such as knowing that European printers between 1860 and World War II used acidic paper. Books made of that paper, which decays quickly, now must be photographed on microfilm to be preserved.