EVERYTHING YOU ever wanted to know about the high price of food in Washington, but didn't know whom to ask, is contained in the latest copy of Washington Consumer's Checkbook, a publication of the Washington Center for the Study of Services.

This 88-page compendium also tells you how to reduce your food costs. When you get through reading, you may decide to do nothing, but you won'it be able to complain that you are helpless or uninformed.

Checkbook, which has rated services in this area for such things as auto repair shops and home maintenance firms, is the brainchild of a lawyer and former director of research for HEW, Robert Krughoff. Nonprofit, with 85 percent of its revenues coming from sales and 15 percent from two foundations, the magazine points out that "shoppers in the metropolitan area do not benefit from a highly competitive food market." Safeway and Giant, it notes, share over 70 percent of the food sales.

Actually, you could learn a lot -- enough to cut your food bill by $400 a year -- just by reading the first three pages of the magazine. They offer three dozen ways to pare your food bill, including some startling advice: "Try Memco. Prices at Memco for our market basket of goods were about 6 percent below prices at the area's major chains.

Try Magruder's. Prices there were about 4 percent below prices at the major chains (more than 18 percent below for produce items) . . .

Also consider Jumbo or GreenbeltCo-op. You may be able to beat the major chains by 2 or 3 percent.

"Among the four major chains, consider Safeway for slightly lower prices. For our market basket, Safeway prices were about 1 percent below Giant's and A & P's and 3 percent below Grand Union's.

The list offers a great deal of other, perhaps, more familiar advice throughout the issue. The advice is offered with a sensible caveat: " . . .not every cost-saving measure makes sense for every shopper . . .if you are a lawyer who bills at $100 per hour, it will not pay you to drive 5 miles extra each week to the supermarket."

In addition to its suggestions on how to cut down your food costs, the magazine explores other facets of the food business: how many supermarkets manipulate customers; whether or not the automated-check stand is beneficial to consumers; how the merchandise and pricing in inner-city stores stacks up against that in the suburbs; why some supermarkets are cheaper than others.

In conducting their price checks, 15 independents and chains were shopped. In addition, the pricing for Giant and Safeway was divided up between District and suburban stores; Safeway Townhouse stores were given a separate category. over 130 items were priced in late summer and late fall of 1978 and then compared with previous pricing surveys done by others since 1975. Checkbook notes that "high priced firms on one survey are high priced on others. . ."

What costs $100 at Giant costs $99 at Safeway, $94 at Memco, $97 at Greenbelt Co-op, $96 at Magruder's, $98 at Shelton's and $106 at Chevy Chase Market.

Without getting bogged down in too much of Economics-101, Checkbook attempts to explain what goes into determining margins, costs and profits. It concludes that while profit differences among the stores are not wide enough to "explain significant supermarket price differences, cost differences can."

The variations, Checkbook concludes, are due to the "fat." In other words, the average costs of supermarkets in Washington are high compared to stores in others parts of the "country."

Checkbook is not able to pinpoint which costs are responsible for the high price of food in this area; it does suggest that a number of things like volume and productivity may account for the differences. At the same time, it notes that even though it has "no way of knowing the extent to which price differences result from productivity differences, the one major exception is checkout technology. Scanning . . . is a major technological innovation, and Giant is far ahead of any of the area's other firms. Interestingly, though, Giant's prices do not reflect the substantial cost savings this new technology is supposed to make possible," a fact Krughoff finds "puzzling."

The magazine, however, is willing to go out on a limb in determing why Memco's prices are much lower than the others: Product mix makes the difference. Each of Memco's stores devotes a majority of its floor space to high-markup, nonfood items."

But Checkbook concludes that if its explanation is correct, there is "one unfortunate implication: There will never be a Memco store in every neighborhood. There is simply not a need to have a department store wherever a supermarket is needed." There are only seven Memco stores in this area.

Most people in the inner city, however, do not shop at Memco, they shop at Safeway or Giant, and Checkbook has concluded that "inner-city shoppers probably suffer most from the difficulty of getting to stores, because of lack of transportation. When they are able to get to inner-city Giants or Safeways, they face about the same quality and prices as surburban shoppers, but less variety and convenient service." Checkbook's conclusions are based on responses from its subscribers as well as professional quantity of fat in ground beef and scientific pricing of market baskets.

Checkbook also explains how many stores manipulate customers:

Staples are spread out to make customers walk past high-impulse items

High-impulse, high-profit items are placed on shelves at eye level while staples are placed at floor level.

High-profit items are displayed next to other items that may be used for the same meal.

High profit items are placed at ends of aisles to catch shoppers as they slow down to go around the corner.

High-profit deli sections are placed at the end of the first aisle because more than 90 per cent of shoppers go by it.

How to avoid the traps and shop smartly? Checkbook notes that there is greater store-to-store variation in the quality and price of produce than in any other department in grocery stores. But it had some confusing results when it compared the ratings of produce by those who shop in the stores with the professional ratings of graders from USDA. While Memco, Giant and the produce markets -- Serio's in Rockville and Soiles at Eastern Market -- scored high with both graders and customers. Magruder's Safeway scored relatively high with customers but low with the graders.

The magazine offers this advice: Memco, Giant and the produce markets "are good bets for quality." In other stores, "you are on your own."

At the meat counter, Checkbook found, shoppers do no face such store-to-store variation. There is very little variation, it says, among the four major chains: Safeway, Giant, A & P and Grand Union. About 30 percent of the survey respondents rated the meat "superior" at those stores. Magruder's got a superior rating from 81 percent of its customers, Chevy Chase Super Market from 86 percent and Sniders 95 percent.

At the same time both Chevy Chase Super Market and Sniders had higher priced meat while Safeway, Memco, Jumbo and Magruder's were at the lower end of the scale.

"in general," Checkbook concluded, "we found that the stores with the higher prices on their steaks tended to have their steaks more closely trimmed."

The differences in the ground beef among the supermarkets, the magazine says are not very important. What's more, after you cook a ground beef patty, ut makes very little difference whether you use regular or lean ground beef. You end up with almost the same amount of fat.

To help cut food costs, Checkbook also suggests:

Buying store brands, particularly Giant's which "rated better than the tested national brands, and A&P's [which] rated almost as well, though Giant store brands tended to have less solids once the packing liquid was drained off.

Purchasing generics, which are cheapest of all."

Shopping in limited-assortment stores where you can save 15 percent or more on national brands.

Purchasing baked goods at day-old stores.

Shopping for some products like cheese, nuts and produce at community stores like Bethesda Avenue Co-op.

Joining a food co-op, where you can save as much as 35 percent on fresh produce.

Neither Safeway or Giant has seen this issue of Checkbook. A spokesman for Safeway said the company "was aware the article was being done, but we have not had an opportunity to look at it yet."

Giant's spokesman said: "this market is very competitive and there are many factors that enter into grocery pricing. For example, all meat sold at various chains is certainly not the same grade so factors like this must be considered."

Checkbook can be found at some newsstands for $4.95. Or it can be purchased by mail for $5.45 from: Checkbook, Suite 406, 1518 K St. NW, Washington, D.C. 20005.