Consumer books: getting your money's worth; Consumers Digest Guide to Discount Buying, by the editors of consumers Digest. Homewood, III: Dow Jones-Irwin. $9.95, $6.95 paperback.; Best Buys '80, from Consumer Guide magazine. Skokie, III: Publications International Ltd. $2.95 paperback.

In this age of belt-tightening, most people are ready to look a little harder to find bargains. To help consumers with this now popular national pastime comes a deluge of books and magazines giving money-saving advice.

The "Consumer Digest Guide to Discount Buying" and Consumer Guide's "Best Buys '80" offer price information and some purchase guidelines for buyers of automobiles and household and recreation items.

The "Guide to Discount Buying" offers shopping advice on more than 25,000 brand- name products ranging from American and foreign cars (both new and used) to vacuum cleaners, photo equipment, and garbage disposers. A "list" (or retail) price and a discount price, which was derived from surveys of discount dealers throughout the country, is given for each product. In addition, the book lists some discount stores where consumers can find the products.

The guide offers some tips for smart shopping. For example, when shopping for camping equipment, watch for off-season sales, look for good buys at department or discount stores rather than at more expensive specialty shops, and use reputable mail-order companies that offer quality goods without the cost of overhead.

This guide spells out the options in each product category. For vacuum cleaners, a reader finds a list of the different types and tells what to look for in design and performance . The book poses questions that consumers should ask while shopping. Does a cannister vacuum cleaner pick up a variety of material? Can the dust bag be easily replaced? Can the machine be carried or stored easily?

The guide also offers best buys, describing the strong and weak points of each product. But the Consumers Digest editors don't point out the bad buys, something most readers would probably like to have included -- especially for the price of the book.

Nearly one-third of the 386 pages are devoted to automobiles. There are breakdowns on such cost details as accessories, listing the dealer costs of different types of axles, edge guards for doors, and deluxe floor mats.

Consumer Guide's "Best Buys '80," a more reasonably priced book, covers much the same territory. IT has a wider variety of product categories, including energy-saving equipment, bicycles, and baby products. In some cases, it does a better job of listing questions a consumer should ask while shopping.

"Best Buys '80" seems a bit more conscious of factors such as safety than "The Guide to Discount Buying." For example, "The Guide," when describing microwave ovens, says that although there were leakage problems when the ovens first came out, manufacturers now adhere to strict government standards and the microwave ovens are perfectly safe to use.

"Best Buys," on the other hand, points out that although today's ovens are built to prevent leakage and that the microwaves cannot produce harmful radiation, the "long-range cumulative effects are yet unknown since the technology is relatively new." This type of statement makes the book seem more plausible.

One weakness of "Best Buys" is that it often doesn't mention as many brand-name products in each category as does "Guide to Discount Buying." And the best bets seem to be a little more expensive than the ones listed in the Consumers Digest book.

Neither book explains how best-buy judgments were made. What factors, such as price, safety, performance, or looks, did they consider? The books are not expected to decide on products for the readers, but one wonders what criteria the editors used to make recommendations.

As reference materials, both books provide valuable information that make comparison shopping easier. But since they list current prices that could change yearly, the books will outlive their usefulness by next year.

Anyone who wants to get the best buy for his or her money will not go out and buy every consumer book that comes along. A cost-conscious consumer looking for a car or vacuum cleaner or microwave oven should research several sources, including consumer magazines, which often have indexes listing when certain products were last evaluated.

Some consumer advice for consumer advice book buyers: Look at more than one. Browse in bookstores foar the book that gives the most complete information on the product of interest.Or check the collection of books at a library.