Above all, there is fear: those who in any manner dare to combat narcotics traffickers live under the constant threat of death. The United States Embassy in Bogota is a bunker, with many diplomats going around armed. President Barco's predecessor, Belisario Betancur, who angered the drug mafia by launching an antidope campaign, is protected by some 40 Government bodyguards. Others have discovered that there is no safe haven, even abroad. Former Justice Minister Enrique Parejo Gonzalez, for example, took up the post of Ambassador to Hungary and, on Jan. 13, miraculously survived an assassination attempt outside his residence in Budapest. The drug bosses had made their point: they could even break through the Iron Curtain. Revenge also eventually caught up with Col. Jaime Ramirez, a respected former antinarcotics police chief, who was assassinated last November, 11 months after he had resigned from office.

Prominent among the few Colombians who have publicly denounced the cocaine ''capos'' have been journalists. In reprisal, 24 have been killed over the past three years. Guillermo Cano Isaza, editor and publisher of El Espectador, Bogota's second-largest newspaper, wrote that ''it is as if the public were itself drugged, unable to see that the power of narcotics traffickers is growing in a colossal way.'' As he drove alone and unarmed on Dec. 17, he was murdered by two gunmen riding on a red motorcyle. His death shocked the country's elite.

COCAINE HAD LONG BEEN AROUND - IT was even fashionable in aristocratic circles in Victorian England - but the special ''talent'' of Colombia's new mafiosos was to convert cocaine into a mass-market drug, cheap enough for students and secretaries, ''safe'' enough for bankers and businessmen. In a remarkably short time, they had seized control of the entire operation, from the purchase of coca leaves and paste from poor farmers in Peru and Bolivia, through the processing of pure cocaine hydrochloride in Colombian laboratories and up to the final retail distribution in the United States. (An estimated 80 tons a year now go to the United States.) Pablo Escobar Gaviria, who tops the world's most-wanted list of cocaine traffickers, is referred to reverently by the people of Medellin as Don Pablo, which seems reasonable for someone said to be worth more than $2 billion. Then there are the Ochoas, also of Medellin: Don Fabio, the father, and his sons Fabio, Juan David and Jorge Luis, whose involvement in cocaine has pushed them into the billionaire class. Carlos Lehder Rivas, who is now awaiting trial in Florida, completes the high command of the so-called Medellin cartel, although he comes from the city of Armenia, 100 miles to the south. Since 1978, this cartel has smuggled an estimated $10 billion worth and more of pure cocaine into the United States.

Why Medellin? First, its strategic location in northwest Colombia and excellent air connections. Then too, the outstandingly good cover provided for clandestine cocaine laboratories by the rolling hills that surround it. The town's industrial tradition guarantees the availability of chemicals needed for cocaine processing. Finally, a slump in its crucial textile sector in the 1970's thrust onto the streets thousands of young men, many of whom became ''mules'' or ''guns'' for the traffickers.

As their empire expanded, the new capos were at first predictable, covering their flanks by paying off local police and politicos and exhibiting their new wealth in cars, aircraft and fine horses, as well as haciendas and mansions. But their real dream was to buy respectability, to be accepted in traditional social circles. And, perhaps to their surprise, Medellin society was delighted to enjoy their wealth without publicly questioning its source.

''Soon the narcos were even seen working out their deals inside the Union Club and the Country Club,'' one local businessman recalls. ''They were being accepted. It was amazing.''

So blatant was the penetration that the descriptive ''narco'' was soon attached to anyone thought to be influenced in any manner by the capos: narco-guerrillas, narco-journalists, narco-judges, narco-politicians, and so on.