"It's no secret that coffee prices are very high," says Giant Food's consumer adviser Esther Peterson as she opens a radio advertisement the supermarket chain started running last week on nine stations in Washington and six in Baltimore.

Mrs. Peterson urges coffee drinkers to cut back on coffee and consider switching to less expensive tea, hot chocolate, Ovaltine, Postum or bouillon. "Remember, coffee is not essential to one's diet," she concludes.

Mrs. Peterson is among supermarket officials, consumer advocates and coffee drinkers across the nation who are displaying their perplexity, amazement and anger over soaring coffee prices by threatening to kick a deeply rooted American habit the cup of coffee.

Nationally advertised brands of ground coffee are already selling at supermarkets for prices approaching and sometimes exceeding $3 a pound, and U.S. Department of Agriculture economists say coffee costs will probably keep rising, at least until early 1978. Retail coffee prices have roughly doubled in the past year.

Giant's anti-coffee ad, which started running Friday, is apparently only the start of the supermarket chains campaign. Mrs. Peterson, who came to Giant afterserving as President Lyndon B. Johnson's consumer adviser, said Giant supermarkets will woon set up displays in store aisles urging shoppers to buy lower-priced hot beverages instead of coffee.

Giant is joining a burgeoning supermarket bandwagon. The large, New England-bases Stop and Shop supermarket chain claims to have the first to post store displays urging its customers to cut back on coffee. It has been running newspaper ads telling shoppers not to buy coffee unless it is on sale. The smaller, Kansas City Justrite chain set up anti-coffee displays in its nine supermarkets in November.

In New York, where city Consumer Affairs Commissioner Elinor Guggenheimer began a coffee boycott Dec. 27, three supermarket chains and at least seven restaurants have already been enlisted in the anti-coffee campaign, according to her aides. The restaurants have cut prices for tea or offer free after-dinner liqueurs to patrons who decline coffee," Guggenheimer said in a telephone interview.

Gimmicks are on eht rise. San Francisco radio commentator Jim Eason has started a "Cafe Oh No" society on his daily ABC network talk show. Coffee boycotters are given "Cafe Oh No" membership cards, which they display when a waiter asks if they want coffee with the their meal.

Last week the spreading drove to cut coffee drinking began to gain momentum in the Washington area where, according to recent Labor Department statistics, shoppers pay more for coffee, on the average, than in any other major metropolitan area in the United States.

Edith Barksdale Sloan, who heads the D.C. Consumer Protection Office, urged Washingtonians to boycott coffee, calling recent price rises "outrageous." She also asked supermarkets to post their previous year's coffee prices next to current prices to help dissuade shoppers from buying coffee. The supermarkets did not immediately respond to her proposal.

"I'm down from eight (cups of coffee a day) to two - which is something of a miracle for me." Sloan said in an interview. "I know how poeple are addicted to coffee. I'mone of those addicts."

Other national and local consumer groups are quickly joining the drive against coffee. An anti-coffee news conference has been scheduled for Monday here by the Consumer Federation of America, the consumer affairs committee of Americans for Democratic Action, the Community Nutrition Institute and Maryland Citizens Consumer Council.

Over the weekend, the Virginia Citizens Consumer Council called for cuts in coffee drinking in a statement headed, "Virginia Consumers Tell Brazil to Sit on It."

Whether these increasing drives to curb coffee drinking or even the spiraling price of coffee itself will cool America's taste for its national brew is far from certain.

George Boecklin, president of the National Coffee Associaltion, a trade group representing roasters and importers, said last week that American boycotts will have no impact on coffee prices unless they are sustained for a long period and widespread enough to attract support in Europe. At present, the anti-coffee campaigns, Boecklin said, are "spotty."

Though still regarded as America's most popular beverage, coffee has been steadily losing its hold on the nation's drinking habits for more than a decade.

According to both government and industry statistics, the slide began in 1962. Annual surveys by the Pan American Coffee Bureau, an industry group, show that Americans of 10 years and older drank slightly more than three cups of a coffee a day on average in 1962. By last winter, the average had dropped to just over two cups daily. An Agriculture Department economist predicted last week that rising coffee prices will accelerate the decline in American coffee drinking.

Analysts of coffee trends say coffee has taken a beating because of booming soft drink sales and changing patterns of American life.

Soft drinks, they say, were promoted more heavily than coffee and apparently are seen as more suited to some of the salty snack foods spawned by the 1960s and 1970s. Americans who ware in a hurry also find it easier to flip open a soda can or bottle than to brew a pot coffee, specialist in coffee note.

Coffee's image has also changed, some analysts say. The blue-collar worker's thermos of coffee is increasing a relic of an earlier era, partly because of improved heating in factories and partly because of newer cold beverages. Coffee also failed to catch on with youth in the 1960s. "They didn't want to do what their parents did," said Jose Gemeil, deputy executive director of the World Coffee Information Center here.

Although the nickel cup of coffee began to fade during the early 1940s and the 10-cent cup largely disappeared in the late 1960s, the rapid rise in American coffee prices began in mid-1975 with a devastating frost in Brazil's southern coffee belt, which killed or damaged hundreds of millions of coffee trees. Brazil normally supplies about a third of th world's coffee exports.

Disasters and political crises also disrupted coffee production in other nations. Civil war raged in Angola, an earthquake struck Guatemala, and too much rain fell in Colombia.

American consumer groups have been especially irked, however, by disclosure last week that Brazil had gained extraordinary profits on its latest coffee harvest. In the past year, it was reported, Brazil earned $2.4 billion on coffee sales, compared with $980 million in 1975.

Rapidly, climbing costs for coffee beans were transformed into rising prices on supermarket shelves and restaurant menus. Businesses in the Washington area have so far reported only slight changes in coffee sales as a result.

At Safeway Stores, which ranks with Giant as one of the two larget supermarket chains in the Washington area, Maxwell House coffee is selling for $3.19 a pound, compared with $1.73 a year ago. Chase & Sanborn is priced at $2.99, compared with $1.65 a year ago. One Safeway house brand, Edwards, sells for $2.45, compared with $1.29 last year.

A Safeway spokesman said last week that shoppers appear to buying more coffee than they did last year, but are switching to lower-priced national brands and to Safeway's two house brands. Safeway's coffee sales in Washington, Maryland, Virginia, Pennsylvania and Delaware increased by 6 per cent in the last 12 weeks of 1976, compared with the same period a year earlier, the spokesman said.Sales of nationally advertised brands dropped by 1 per cent, however, with one leading brand falling by 26 per cent. House brand sales rose by 10 per cent, the spokesman said.

The Macke Co., which supplies coffee vending machines to government and business offices in the Washington area, has boosted coffee prices on most of its machines by a nickel to 20 cents a cup. J.B. Magner, the company's manager, said nevertheless that coffee sales have increased slightly.

At the Georgetown Coffee House, a busy Wisconsin Avenue gourmet shop where coffee now sells for more than $4 a pound, floor manager David Jacobs said sales have remained steady, although some new coustomers are buying half pounds instead of pounds of coffee. "They're not happy with the price, but neither are we," Jacobs said.

At Sholl's cafeterias, which pride themselves on low prices, the cost of a cup of coffee was increased from 6 cents to 10 cents last spring. Even Sholl, the owner, said last week that patrons are drinking as much coffee as ever." He said he has no plans to charge more for coffee.

While no clear trend has emerged interviews with coffee drinkers turn up repeated examples of consumers who say they are cutting down on coffee because of its price.

"We've cut coffee consumption back 50 per cent," said Lillian Hartung, who lives in Reston. She and her husband, a mathematician, are switching to tea in the afternoon and evening. "I don't want to be taken advantage of," she added. "It's like the price of oil."

According to data compiled by the U.S. Bureau of Labor Statistics, shoppers in the Washington area paid more for ground coffee in recent months than in any of 23 other metropolitan areas surveyed by the bureau. In November, the latest month for which figures are available, the average cost of coffee in Washington was $2.68 a pound, compared with $2.23 nationally.

Coffee cost $2.20 a pound in Baltimore, $2.36 in Boston, $2.21 in Chicago, $2.47 in Dallas, $2.03 in Houston, $2.01 in Los Angeles, $2.36 in New York, $2.32 in Philadelphia, $2.57 in St. Louis, and $2.02 in San Francisco.

Why shoppers paid higher prices for coffee in Washington in unclear. Some businessmen familiar with food prices said coffee may be sold at or below cost as a promotional gimmick in other areas, while not in Washington. Also, there may be less competition among nationally advertised coffee brands in Washington because Folger, one of the nation's leading coffee brands, is not marketed in the Washington area. Consumer groups charged that there is insufficient competition among supermarkets in Washington over many food products, including coffee.