Frank Tweddle Granda was seated in the first class section of an Aeroperu fight about to leave for Guayaquil, Miami and New York, when two Peruvian customs agents boarded the plane March 13. The agents asked Tweddle to disembark to "resolve a tiny problem with your luggage."

Inside Lima's airport, Capt. Manuel Prieto Salas confronted Tweddle, a retired Air Force general and former president of Aeroperu, with one of the suitcases he had checked aboard the flight.

Inside the suitcase, carefully wrapped and hidden beneath shirts monogrammed with Tweddle's initials, were three small packages containing more than 11 and a half pounds of pure cocaine -- worth more than $4 million at retail on U.S. streets.

It was one of the largest drug seizures in Peruvian history and the first time that a high-ranking member of Peru's military elite had been charged with trafficking in cocaine.

The arrest was also the first in a series of steps the Peruvian government has taken over the past several months to clamp down on the $500 million yearly cocaine trade, which now rivals oil and copper as an export earner here.

As in Mexico and Colombia, where the drug traffic generated billions of dollars a year before the governments decided to act. Peru's military authorities now see the local cocaine industry as threatening their control over whole sections of the country.

The military also knows that cocaine money is beginning to corrupt poorly paid policemen and soldiers and that the health of more and more Peruvian teen-agers is being affected by the growing use of coca plants, a highly toxic and addictive substance that once was exclusively for export.

In addition to stepping up surveillance at Lima's international airport, where Tweddle was arrested, the government recently sent 900 armed policemen on a 20-day search and destroy mission in Peru's principal coca-producing region and is now beefing up police and paramilitary units assigned to the anti-cocaine effort.

"I think the Peruvians are serious about stopping the narcotics trafficking," a U.S. Drug Enforcement Agency official here said recently. He was not overly optimistic that the belated campaign would more than inconvenience the rich and now well-organized drug traders in Peru, the world's largest producer of coca leaves.

Tweddle, whose passport showed he had traveled to Miami nine times during the year before his arrest, is still in jail awaiting trial.

As recently as six months ago, these observers said, if an active or retired general were caught smuggling drugs, he would not have been prosecuted. Tweddle faces up to 15 years in jail if he is found guilty.

According to DEA estimates, Peru produces about 44 million pounds of coca leaves a year for the international trade. The leaves are refined into coca paste and coca base in Peru before these more valuable substances are smuggled to Columbia, where the base is transformed by a chemical process into cocaine.

The DEA has become more active in Peru. The United States is providing about $50,000 to help Peru combat the cocaine industry -- a drop in the bucket considering the resources available to the traffickers.

The highly respected Andrean Report, a monthly economic journal published in Lima, recently estimated that more than 900,000 of Peru's 17 million citizens are directly involved in the cocaine trade -- most of them peasants who grow coca in the jungle areas of northern Peru near the town of Tingo Maria, fondly known to local residents as "Snow City."

The peasants receive only about $3.50 a pound for coca leaves, a minute fraction of the leaves' value once they are refined into pure cocaine, which sells for about $2,800 an ounce in the United States. But it still provides a small fortune in rural Peru.

The prosperity that has come with the illicit coca production is evident in Tingo Maria, a town of 35,000 that has three car dealerships and 10 hotels. Its several dozen appliance stores do a brisk business in television sets even though there is no television transmission in the area. The number of cars, trucks and motorcycles sold in Tingo Maria is second in Peru only to Lima, a city of more than 5 million.

"Commerce is run on coca money," a police official in Tingo Maria said recently. "When we make a raid, business drops and this town is dead."

Coca growing is not actually illegal in Peru. In 1978, however, the government issued regulations saying that it would seize and destroy any coca farms larger than 24 acres after a two-year grace period. The March raid by 900 policeman was designed to demonstrate that the government was serious, although reports filtering back to Lima indicate that the national police managed to destroy only about 1,900 acres during the 20 days they remained in Tingo Maria.

"And what about the 141,600 acres remaining?" asked Caretas, a weekly magazine that sent a reporter along on the raid.

DEA officials in Lima said the raids, were just a start and that the government has plans for further missions that will demonstrate to the peasant farmers that they had better begin switching their fields from coca to other crops -- or face confiscation and jail terms or up to two years.

Gen. Rolando Llamos Oliveros, the head of Peru's drug enforcement agency, said one of the primary reasons the government has stepped up antidrug activity is because a growing number of Peruvians, especially teen-agers, are using coca-based substances.

It is not unusual to see teen-agers in Miraflores, "wealthy Lima residential area, lightning up "little pistols," marijuana cigarettes doused with coca paste.

Other informed observers say the military has also become increasingly concerned over drug money beginning to corrupt the armed forces and that the military's already tarnished image was being further blackened because of ranking officers' alleged involvement in trafficking.