Marcos Cadavid, an alleged Colombian cocaine wholesaler, was sentenced by a federal judge here yesterday to a 15-year prison term on charges of arranging to supply millions of dollars in drugs to a District-based narcotics ring.

Judge Thomas F. Hogan imposed the maximum sentence on Cadavid, who was convicted by a U.S. District Court jury last month on a single conspiracy count. He also fined Cadavid $25,000.

"The effects of widespread use of cocaine are well known," said Hogan, citing Cadavid's alleged role in a "sophisticated, coldly calculated" and profitable drug-smuggling scheme.

Cadavid, 43, was among the first Colombians to be extradited last January by the South American government under a recent treaty with the United States aimed at cracking down on narcotics traffic. U.S. Attorney Joseph E. diGenova praised Colombia yesterday for "superb cooperation" in the case.

In a brief statement before being sentenced, Cadavid contended that he had been singled out for punishment because of crimes allegedly committed by other Latin Americans, including the recent slaying of a U.S. narcotics agent in Mexico. Cadavid spoke in Spanish through an interpreter.

Hogan rejected Cadavid's assertion, saying that Cadavid was "not made a scapegoat in any sense of the word." Melvyn Kessler, Cadavid's Miami-based lawyer, said the conviction will be appealed to the U.S. Court of Appeals.

In a six-day trial conducted under unusually heavy security, Cadavid was found guilty of conspiring to import and distribute cocaine between 1976 and 1983. Cadavid did not take the witness stand at the trial.

According to the prosecutors, Cadavid and another Colombian, Armando (The Hammer) Marulanda, formed a Miami connection that supplied cocaine to a D.C.-based drug ring at meetings in a Miami apartment. Marulanda is described as a fugitive.

Assistant U.S. Attorney Roger M. Adelman said during yesterday's hearing that Cadavid had taken part in hundreds of sales of high-quality cocaine worth $35 million. Prosecutors later described that figure as the wholesale value of the drugs and put their "street value" at $175 million.

Seven members of the narcotics ring, including its leader, Lawrence G. Strickland Jr. of Bethesda, have pleaded guilty. Four others, among them former lobbyists Fred B. Black Jr. of Washington, were convicted on federal charges last month.

Black and former Riggs National Bank vice president William G. Hessler are now on trial on fraud and racketeering charges in connection with alleged laundering of the ring's profits.

DiGenova said that the investigation has focused on several other states, including Texas and California. In Texas, he said, six alleged traffickers have been arrested and two of them have pleaded guilty.

Kessler, Cadavid's lawyer, had urged Hogan to limit Cadavid's sentence to eight years' imprisonment, arguing that the shorter term would be "more than adequate punishment." Prosecutors said that Cadavid could be expected to serve at least 10 years of the 15-year term before becoming eligible for parole.