Federal agents said yesterday that they smashed a South America-based cocaine-smuggling ring said to be importing as much as 15 tons of the drug into the United States annually and selling it nationwide at an estimated street value of $12 billion.

Agents said they arrested more than 70 of the 81 suspects in the case, conducted by the Organized Crime Drug Enforcement Task Force for 18 months.

The ring operated distribution outlets throughout the United States, and an indictment said sales operations were set up in Miami; San Diego; Los Angeles; San Francisco; Dallas; Sun Valley, Idaho; Portland, Ore.; New York; Atlanta, Hawaii and Guam.

Charges in the indictment and separate criminal complaints were brought against 81 persons who allegedly worked in the ring, reputedly headed by Peruvians Agustin Fernando Maurtua, 26, and Jose Antonio Ledgard, 27. Both were arrested last week.

The indictment said Maurtua headed the West Coast distribution network from his home near San Diego. Ledgard allegedly headed the East Coast distribution operation from Miami.

U.S. Attorney Peter K. Nunez said four major figures in the case will be charged under the Continuing Criminal Enterprise Statute designed to prosecute major narcotics traffickers. Also singled out were Michael Jay Sullivan, 27, of Del Mar, Calif., and Frank Len Jackson of Encinitas, Calif.

Sixty-eight of the 81 suspects, mostly San Diego residents, were charged with narcotics offenses.