If you eat a steady diet of peanut butter and jelly sandwiches, fresh apples and hot coffee, you spend two to three times as much money at the grocery store as you did six years ago.

But if you subsist on bacon and eggs, you actually pay less than you did in 1973 - bacon prices are down 25 percent at many of the Washington area's biggest stores; egg prices have fallen nearly 7 percent.

With the publication of the latest consumer price index yesterday, the government said that food prices here have gone up 63.6 percent since 1973, but a survey of 40 common supermarket items yesterday showed that the amount of inflaion in an individual grocery bill all depends on what you buy.

Hunt's canned whole tomatoes, fro example, are up 345 percent at the Giant food chain over 1973. By contrast, whole chickens, which cost 59 cents a pound at Giant in 1973, cost the same there yesterday.

Where the first Washington Post food price survey was done six years ago, rising food prices had so incensed consumers that they began talking about conducting boycotts and forming food co-ops. That anger peaked in the mid-70s and, according to a national survey made for the food industry, reached a low point in March 1978. But outrage is climbing once again, the survey showed.

Price increases found in The Post survey may help explain why.

Of the 40 items checked at a Giant Food supermarket, 36 bore higher price tags. One - the chicken - was the same as before. A second item, frozen haddock, was not available. Only two foods, bacon and eggs, were less expensive.

Briggs sugar-cured bacon was $1.49 a pound, down 30 cents from the earlier level. Large eggs were 85 cents a dozen, or six cents less than before.

Although prices for those items varied slightly from one chain to another, the general trend was the same.

At Grand Union, for example, bacon was $1.19 a poud - 40 cents less than the 1973 price.A dozen eggs sold for 85 cents, the same as six years ago.

Prepared foods such as cereals and canned vegetables showed some of the sharpest increases.

At Safeway, the price of a 12-ounce box of Kellogg's corn flakes has more than doubled. It was 29 cents before; now it is 73 cents. The 15-ounce box of Special K cereal has climbed from 77 cents to $1.53.

Green Giant peas in a 17-ounce can now cost 50 cents at A & P. The item was 25 cents six years ago.

Fresh produce also climbed dramatically over 1973 levels, the survey showed.

Apples are more than double their old price. They cost 69 cents a pound now at Giant and Safeway compared to 25 cents a pound in 1973. And Grand Union, which once sold Delicious apples at 29 cents, now charges 69 cents.

Beef costs more, but the increases are less dramatic than for some other grocery items.

Boneless round steak, for example, has gone from $1.89 a pound to $2.84 a pound - a 50 percent increase - at Giant. Lean ground beef is $1.69 a pound, compared to $1.19 before, a 42 percent increase.

At most stores, coffee has tripled in price since 1973. Giant now charges $3.25 a pound for Maxwell House regular grind, compared $1.10 before. At Grand Union, that same brand has increased to $3.79, up from $1.10. Safeway's price has climbed to $3.79 from $1.03. The A&P sells coffee for $3.79, compared to $1.07.

The price at Memco now is $2.66, up from $1.12.

Measuring today's prices against yesterday's is sometimes complicated by changes in package sizes. The trend generally is toward smaller containers and larger price tags, a phenomenon often referred to in the trade as the "shrinking candy bar."

The 24-ounce loaf of bread at Giant has shrunk to a 22-ounce size, while its price has expanded from 32 cents a loaf to 40 cents yesterday.

Most painful for many shoppers is the marked increase in such old-fashioned basics as the peanut butter-and-jelly sandwich. The price of an 18-ounce jar of Peter Pan peanut butter has more than doubled at four stores. It has gone from 71 cents to $1.49 at Giant, A&P, Safeway and Grand Union. Memco has increased its price from 71 cents to $1.37.

Shoppers watching the price changes from day to day appear to be adjusting their buying habits to find the best bargains, supermarket officials said.

"They're going back to basics," said Don Vaillancourt, a spokesman for Grand Union. "They're buying fewer convenience foods and more basic staples. They're also downtrading on meats, buying more poultry and the lesser cuts of pork and veal."

In addition, turkey has become a year-round food, rather than just a Thanksgiving special, he said.

A national marketing survey prepared for the Food Marketing Institute identified some of the actions that consumers are taking in their effort to economize.

Seventy-six percent of the persons interviewed said they are using more leftovers now than they did in the past. Only 69 percent said they were doing that in the last such survey.

Other actions included: doing more meal planning, 61 percent now, compared to 53 percent in 1974, cutting down on entertainment, 41 percent now and 33 percent before, doing more baking, canning and freezing, 49 percent now compared to 48 percent before.

Consumers also are eating less in an effort to keep food bills down, the survey said. Twenty-five percent now serve less food at meals. Five years ago only 21 percent were doing that.