RON JAFFE is looking forward to later this month when a new Tom Clancy thriller comes out The Sum of All Fears." Mr. Jaffe, as marketing director for Walden Book Company Inc., has a clear interest in ensuring that book buyers rush out to their local chain store to pick up a copy of this latest thriller from one of the best-selling authors in the United States.Beyond Tom Clancy, a new Stephen King novel comes out in late September; a new Sidney Sheldon novel is published later this month; Danielle Steel will have another book out in November. Finding a book store to buy one of the new crop of books shouldn't be hard. Walden blankets much of the US with its 12,000 stores, including some 25 giant "superstores." Walden's main rival, Barnes & Noble Inc., has some 1,200 stores spread around the US, including 750 B. Dalton stores, 53 Barnes & Noble outlets, 45 Doubleday stores, 11 Scribner's Bookstores, and 35 Bookstop/Bookstar outlets. On Aug. 15, Barnes & Noble is opening its latest (and fourth) "superstore," in Burnsville, Minn. This suburban Minneapolis outlet will carry over 100,000 titles, compared to 20,000 titles found in a B. Dalton Store, says Kate McDonough, a vice president with Barnes & Noble. "We're excited about the new store and we're very excited about the new fall book season." "It's true that many book sellers have felt the impact of the recession ... But we're finding that people are reading more and buying more books - particularly children," Ms. McDonough says. Anticipating the fall book season - which will be in full gear by mid-September - is now the primary topic in publishing and book store circles. Behind all the "official" upbeat euphoria, there is some concern. Last year's sales were sluggish, not much over those of 1989. "The recession did have an impact on sales," says Judith Platt, spokeswoman for the Association of American Publishers in Washington, D.C. "The recession particularly hit elementary and secondary textbooks, which is usually a very hardy market." As spending by local school districts dropped, so too did purchases of textbooks, which were up only 2.1 percent, compared to a (more normal) gain of 11 percent for 1989 over 1988. Overall book sales in 1990 totaled $15.4 billion. That is a "modest" increase of 5.3 percent from 1989, says Ms. Platt. In 1989 sales grew almost 11 percent over 1988. The biggest gain in 1990 - up 8.1 percent - came from college textbooks. Trade books climbed 7.4 percent; mass market paperbacks were up 4.9 percent; book club sales rose 3 percent. Clearly, the book publishing and book store industries in the US have a great deal to gain from an end to the recession and a pronounced restoration in consumer spending. The publishing industry has been facing intense turmoil as the giant conglomerates that control most of the publishing houses continue to streamline operations. A number of front-office heads have been shifting jobs from one company to another in past months; the corporate owners are cutting costs to increase profits - even while the ad vances paid to the authors of new books continue to increase. Some companies have raised prices on books. Most of the major publishers are now corporate entities; Simon & Schuster, for example, is owned by Paramount Communications Inc.; Warner Books Inc. is owned by Time Warner Inc.; Bantam Doubleday Dell is owned by Bertelsmann AG, a German company; HarperCollins is controlled by News Corporation; Random House Inc. is owned by Advance Publications Inc. And while the major publishers have become economic giants, so too are the large book chains. Barnes & Noble is privately held, though essentially controlled by investor-businessman Leonard Riggio; Walden Books is owned by K-Mart Corporation. Will the upcoming fall book season be successful? "Our sales are running very strong," insists Mr. Jaffe of Walden. The important point, says Jaffe, is that "the fall product list is the best that we've seen in years. That's going to bring people into the book stores."