Attorney General William French Smith said yesterday that four fugitives wanted on drug charges in the United States have been returned by Colombia under a 1982 extradition treaty, the first time Colombian nationals have been extradited under the treaty.

Officials said they regard the action, approved by the Colombian Supreme Court and by President Belisario Betancur, as a breakthrough in efforts to control international drug activities. There had been fears that nationalistic feelings against sending Colombians to the United States and threats of violence against officials could hamstring extraditions.

Smith identified the four extradited persons as Marcos Cadavid, charged in the District of Columbia with conspiracy to import and distribute cocaine from Nov. 1, 1976, to the end of 1982; Hernan Botero-Moreno, charged in Miami with participating in a multimillion-dollar money-laundering conspiracy from late 1979 to October 1980; and two brothers, Ricardo and Said Pavon Jatter, charged in Miami with various counts of conspiracy to import and distribute cocaine and conspiracy to distribute the proceeds of narcotic drug sales.

Smith said the four were flown from Bogota to Homestead Air Force Base, Fla., on a Colombian C130 plane with an all-Colombian crew. He said Cadavid will be arraigned in U.S. District Court here Monday, the other three in U.S. District Court in Miami Monday.

The United States does not sponsor a large-scale drug-eradication program in Colombia but has sought the extradition of more than 40 persons accused of drug trafficking. According to reports, some drug dealers, who command widespread influence there, have responded with threats to kill U.S. diplomats and citizens.