BOUGHT ANY cranberries lately? Checked the price on a jar of peanut butter? Read the label on mozzarella cheese? Tried to decide which ground beef to buy?

The supermarket is a constant source of surprises from the moment you enter until you fork over $40 for two bags of groceries . . . without meat. This season's surprises are among the most astounding since coffee shot up to $6 a pound.

The United States is in the midst of a tremendous peanut shortage, which is just beginning to make itself felt at the retail level. Freshly ground peanut butter in one local supermarket went from $1.05 a pound to $2.79 within two weeks. Even a 40-ounce jar of commercial peanut butter is selling for $3.89 now. In some parts of the country peanut butter is being rationed.

What are mothers going to feed their kids for lunch? What are we going to use to replace the expression: "It's peanuts!"

One local supermarket official predicted that "people are going to be lucky to be able to find peanut butter," but he didn't want his name used. "If you quote me, we'll have a run on peanut butter." From a look at the shelves, that may have happened already.

The peanut shortage is due to this summer's drought, which caused the peanuts to whither on the vine, reducing the harvest by 42 percent. Import quotas on peanuts were lifted earlier this month, but apparently there aren't many peanuts to be found abroad, either. The shortage won't be alleviated until the next peanut crop is harvested in the fall of 1981.

But how do you explain what's happened to cranberries? Bagged in a "new convenient size," which is 25 percent smaller than last year's presumably "inconvenient" size, a pound of them is double last year's price. This appears to have infuriated "hundreds and hundreds" of people who have flooded Ocean Spray, processors of 85 percent of the cranberries sold in this country, with complaints. This letter from an Arlington, Va., resident is, perhaps, more strongly worded than others, but the message is the same:

"Who do you people think you are? Who do you think I am that you can gull me with your "new convenient size" of cranberries? What gives you the idea I don't know whose convenience you had in mind when you raised the price and cut the weight?

"You took me for one package, but it sure won't work again."

In response to such consumer complaints Ocean Spray offers a number of reasons for the high price, some of them contradictory.

The consumer relations department wrote to one customer: "Please understand that for the past few years there has been a shortage of fresh cranberries. . ."

But the manager of public affairs, Skip Colcord, said in a phone interview, that this year's crop was "very good, better than last year's. But still," he said, "there are not enough cranberries in relation to the demand. The primary reason is that America has developed a very strong appetite for cranberry drinks. Drinks take up most of the cranberry crop, unlike the situation 20 years ago when most of the cranberries went into sauce and fresh produce."

Colcord also said that the method for harvesting cranberries to be used in processed foods is more efficient and less costly than the method used to harvest cranberries for the fresh market because fresh cranberries "must be perfect."

Prices of processed cranberry products -- the drinks, relishes and sauces -- "have only kept pace with inflation," Colcord said. Prices for fresh cranberries were up "almost 30 percent" at the processor level. If that is the case, Washington supermarkets have tagged an enormous profit margin. Last year's 16-ounce package of cranberries at 49 cents is this year's 12-ounce package at 69 and 79 cents (92 cents to $1.05 a pound).

Even though the fresh cranberry supply has not kept up with demand the last three years, for Ocean Spray's 50th anniversary, the company sent four foreign chefs on a year-long cross-country tour of the United States to promote fresh cranberries. "With any business," Colcord said, "you have to work for the future."

So growers are planting more vines, but it will take three to five years for them to bear fruit.

Colcord admits the downsizing, also known as packaging to price, has been a "no-win situation. We're definitely going to take a look at going back to a 16-ounce package. We're very consumer oriented. Very concerned, obviously." 1

In the meantime you might want to try pear relish with your turkey.

Speaking of turkeys, is there anyone out there who doesn't know by this time that Swift's Butterball turkeys contain no butter?

But now many people know there's no cheese in the new imitation cheeses that are making serious inroads into the cheese counter? Two new imitation mozzarella cheeses sit right next to the real mozzarella. Some of these imitation cheeses are sold as an alternative to natural cheese for those who are on low cholesterol and low saturated fat diets. Thus, when a mozzarella, Fishers Pzza-Mate, says "made with vegetable oil" on the front of the package, it might lull someone into thinking the cheese was low in saturated fat. But the ingredient statement on the back of the package lists coconut oil as one of the oils that may be used in the product. Whether or not coconut oil is used in the particular package of Pizza-Mate cheese is something the consumer will never know. But coconut oil is almost twice as saturated as lard.

Imitation mozzarella cheese is less expensive than natural mozzarella cheese. It has approximately the same amount of fat per serving and the same number of calories. What really distinguishes it from real cheese is the taste. Melted on the top of a piece of bread, both Pizza-Mate and Pizza Pal from Unichef (which doesn't contain any coconut oil) were judged to taste almost inedible. Perhaps with lots of tomato sauce and a heavy dose of strong spices, herbs, garlic and onion, the taste would not be so obvious. If you have to substitute imitation mozzarella for the real thing because of health, be sure to read the list of ingredients carefully. After you taste it you may decide to do without.

Another change in the supermarket can be found in the ground beef section. Several years ago supermarkets agreed, on a voluntary basis, to stop labeling ground beef by the cut from which it was supposed to have come -- ground chuck, ground round, ground sirloin -- on the theory that customers could not tell how much fat such a cut contained. Instead many supermarkets agreed to label the ground beef according to its fat content. Some call it "regular," "lean" and "extra lean" (Safeway has only two grades; the one with the least amount of fat is called premium); some named with the ratio of lean to fat. For example, ground beef that is 80 percent lean and 20 percent fat is called "80-20." By federal regulation ground beef can have no more than 30 percent fat.Within the last year both Safeway and Giant have returned to some of the old nomenclature for ground beef. Giant has ground chuck; Safeway sells ground chuck and ground round.

Safeway's regular ground beef contains 24 to 26 percent fat and costs $1.69 a pound; premium contains 16 to 18 percent fat and sells for $1.99 a pound. The chain's ground chuck is 20 to 22 percent fat and sells for $2.19 per pound; the ground round is 14 to 16 percent fat and sells for $2.59.

Giant's regular ground beef is 28 percent fat and sells for $1.69 per pound; lean is 23 percent fat and sells for $1.89 a pound; extra lean is 18 percent and costs $1.99 per pound; ground chuck ranges from 12 to 22 percent fat and costs $2.19 per pound.

Are ground chuck and ground round really worth the significant difference in price?