I WAS SITTING in a darkened living room in Arequipa, Peru, 4200 miles due south of Cambridge. Today Jenny, the oldest daughter of this Peruvian middle-class family, turns 20 years old. For her, it will be the most important day of the year. Various female cousins are stationed on couches, exchanging news of family and friends in hushed tones, with an eye cocked to the window. Lest Jenny spoil her surprise party by entering unannounced, her 16-year-old sister Lillian is poised to intercept her. But Lillian's alertness is premature. An hour passes with muffled laughter and continuous conversation. Though guests were sternly warned to be here at seven sharp, the easygoing hora peruana ("Peruvian time") prevails. An hour and a half later only a few more guests have trickled in.

While they wait, three-year-old Galo plays with his wooden top. Most young peruanos have tops; resembling a large radish in shape and size, the top is thrown like a yo-yo with a flick of the wrist and spins upright even in an unpaved road.

After school, boys with tops appear on every corner, dressed without exception in white shirts, gray pants, and gray sweaters. Girls wear gray skirts. The uniforms are required by law in both private and public schools to reduce class distinctions among students. But by casting their tops into the dusty street, these boys mark themselves unmistakably as lower class. Jenny's younger brother also owns a top, but only for use inside the house.

At age three, Galo cannot yet spin the top. He has just begun to cry, and the cousins to argue, when the uproar is suddenly suppressed. Two hours late, the birthday girl has arrived. As Jenny enters, the room is flooded with light and congratulations are shouted. Jenny attempts to look surprised but only succeeds in looking pleased.

After a month in Peru, I am no longer surprised when the party begins to the sound of American rock--in this case "Money Honey" by the Tubes. Along with the Colombian cumbia rhythms popular throughout South America, teenagers buy English-language 45's by the Bee Gees and the Ohio Players. The biggest American dance is the "bump bump," pronounced "ban ban" and featured in a prominent television commercial for stylish sweaters. Many Peruvians believe it is a Peruvian dance. Teenagers are just as ready to break into a wild twist powered by Buddy Holly's "Rock Around the Clock." The Hustle, on the other hand, has a limited future in Peru. The need which the Hustle filled in the States for a dance in which the partners touch, a dance with complicated variations on a single step, simply does not exist here. The cumbia, the parrandera, the marinera all fit the bill and all are actively danced; even, on occasion, the tango. As the party progresses, however, dancers settle into what is most familiar--the wiggling shoulders, swinging arms, smooth steps, and sideward swaying of the hips that characterize the cumbia.

LIVING WITH this middle-class family, it is hard to remember that Lima is under curfew after an attempted coup; that rumors of an uprising in Trujillo and the burning of the Sears building in the capital city had reached my ears this morning; and that a week ago, four tanks with rubber treads filed out of the barracks two blocks away headed for the center of Arequipa. No one talks politics at the party. As a university student who had been in Chile before, during, and after the Allende regime told me, "Politically Peru is 20 years behind Chile. Everyone minds his own business. The Peruvians are not a political people."

They are, however, a romantic people. During the evening I learned the story behind the song "Maria Bonita," which is 30 years old and more popular than ever in this latest version sung by Julio Iglesias. The songwriter, Augustin Lara, "one of the ugliest men in Mexico," fell in love with Maria, the most beautiful woman. "They married but she had other loves. You can't love as much if you have others."

In return for a guarded description of American social mores, which are referred to in Peru as "free love," I was told that "every man wants to be the first man in a woman's life and every woman wants to be the last woman in her man's." Unfortunately, it doesn't always work that way, because "men are hummingbirds," fickle Don Juans.

In my hosts' home, a variety of alcoholic beverages served at the party was unusual. Most of the time we drank nothing stronger than Inca Kola. A piss-yellow soft drink with the taste of bubble gum, Inca Kola manages to more than hold its own against the foreign invader, Coke. In Peru soft drinks are chugged rapidly at a gulp. For this style of drinking Coca Cola has too much gas, something which the company's South American executives either don't know or are unwilling to change.

The one time we had drunk liquor en casa was on the Fourth of July. On Independence Day we toasted the United States with a bottle of the local brew. Each member of the family hugged me in congratulations for "my day." Then Papa and I solemnly consumed the revered--and apparently much-feared--beverage in front of a television screen on which appeared successively, shots of an unidentified parade, people milling in Central Park, and finally, Nelson Rockefeller greeting the people in his own correct, methodical Spanish, testifying to the greatness of two great peoples on this great day.

On another "great" day eight years ago, Peru's leftist military junta took power. Shortly after this change came agrarian reform, closer Peruvian links with the Soviet Union, and the expropriation of U.S. copper and oil interests. The drop in food production after the land reform, however, sent high prices even higher, threatening the popularity of the government. As a result Juan Velasco, "the father of the Peruvian revolution," was replaced in 1975 by the less socialistic Francisco Morales. The Morales government tilts toward the center, encouraging foreign investment in Peru with better terms and repayment for expropriated holdings. Perhaps this explains Rockefeller's Fourth of July appearance on government-owned television.

While the government has swung left and right in the last eight years, the entertainment media have always been dominated by America. I did not expect to see "The Streets of San Francisco" and "Barnaby Jones" on Peruvian television, but I did--along with "The Munsters," "Maverick," and the favorite of my host family and President Ford, "Policewoman."

The morning after the party, Jenny had a request: would I help her write down the words to an American hit song she admired? Listening carefully for the first time to "Love Hurts," by Nazareth, I realize that it is powerful, thoughtfully-structured music. Peruvian girls are crazy about it. I cannot condemn this "cultural imperialism," if that's what it is, because it is perpetrated by the music I grew up on. Others might have been weaned on Prokofiev's Peter and the Wolf, cello lessons and madrigal singing around the family piano, but I spent my Wonder Years humming along to Diana Ross singing "Baby Love." The future is unpredictable; perhaps in another few years Peru will swing left again, and schoolchildren will be required to sing the "Internationale," but in the meantime, "Love Hurts" is taking Arequipa, Peru by storm.