Outlet shopping is a $6 billion annual business and provides a $4 billion savings to consumers, according to the author of the second edition of "The Joy of Outlet Shopping."

And it's growing. The 132-page guide to outlet shopping centers lists more than 250 outlet centers, 25 percent more than the first edition just a year ago. It also lists where and when more than 100 outlet centers under construction plan to open.Outlet stores, where manufacturers sell direct to the consumers at discounts of 20 to 70 percent, are nothing new. A century ago they were confined to milltowns in the South. They were known as factory stores or mill stores.

Then, about 15 years ago, the first outlet center, where many stores were clustered for shoppers' convenience, opened in Reading, Pa. They gradually moved West, reaching California in 1988. Now they're in 39 states and Canada.

Outlet stores are what their name implies. They provide an outlet for a manufacturer to dispose of excess merchandise, from canceled orders to factory overruns.

While there are many outlet stores for housewares, men's and children's wear, leather goods and shoes, the bulk of the shopping is for women's apparel. Familiar labels include Adolfo II, Adrienne Vittadini, Anne Klein, Calvin Klein, Chaus, Ellen Tracy, Esprit, Harve Bernard, J. Crew, J.G. Hook, J H Collectibles, Jaeger and Jantzen.

- The guide, written by Terry Dunham, who has tracked outlet retailing since 1979, is $4.95 from JOY, Box 7867, St. Petersburg, FL 33734.