A 54-year-old District man whom prosecutors described as the central figure in a major heroin distribution ring supplied by Nigerian nationals was sentenced in federal court here yesterday to 12 to 38 years in prison and fined $100,000.

U.S. District Judge John Garrett Penn imposed the sentence on Eddie Adair, who operated the drug distribution ring out of a vacant motel he owned at 11th and U streets NW.

"You seemed to have have no problem in profiting on the misery of others," Penn told Adair.

Adair, who was convicted May 22 of drug conspiracy and racketeering charges, maintained throughout the nine-week trial that he was actually a watermelon salesman and that it was watermelons, not drugs, he was discussing on tape recorded wiretapped conversations played during the trial. He repeated the claim yesterday.

Then, likening himself to the biblical prophet, Adair asked Penn to "protect" him like Daniel in the lions' den.

Assistant U.S. Attorney William J. O'Malley Jr., who prosecuted the case along with Darryl W. Jackson, told Penn that Adair, of 1027 Euclid St. NW, was "plain and simple" in the "filthy, greedy despicable business" of dealing in drugs.

O'Malley said Adair had been distributing heroin for three years and for "many, many years before that" was selling narcotics such as Preludin. He had had no "lawful, legal source of income" for years prior to his arrest last August, the prosecutor said.

In addition, O'Malley said, Adair had not "attempted to file income taxes since 1975" despite earning enough money to buy eight developed properties, including the motel, and two vacant lots within two blocks of the new Metro Green Line.

Adair's attorney, Arthur Levin, told the court that Adair was a carpenter who for 30 years had done renovation work on his own properties and for others.

According to court documents and testimony presented during the trial, Adair earned between $10,000 and $15,000 a day through his heroin operation, which employed five or six runners who sold the drugs for him.

Although D.C. police had been aware of Adair's activities for several years, they had been unable to gather enough evidence to make a case against him.

Even after an informer said he had bought heroin from Adair several times, the FBI was unable to penetrate Adair's operation because he would only deal with people he had known for several years.

Much of the evidence in the case was obtained through court-ordered wiretaps on telephones at Adair's home and motel and a bug that was placed in the motel office. Later wiretaps were placed on the telephones of two Nigerian nationals who supplied Adair with heroin through an international drug trafficking ring based in The Hague, according to court documents.

Three Nigerians charged with Adair were sentenced last week to prison terms of five to 15 years on drug conspiracy charges. Two women, described by prosecutors as Adair's girlfriends, were given lesser terms.

In addition to the heroin distribution charges, Adair still faces 17 criminal counts involving cocaine distribution. He will be tried later on those charges.