Three Nigerian nationals convicted of importing heroin into the United States in the first trial that proved the drug comes into Washington through a "Nigerian connection" have been sentenced by a federal judge here to the maximum five-to-15-year term and fined $20,000.

"The evidence was overwhelming that you were involved in importing drugs . . . with no consideration for the harm you were doing to this country," U.S. District Judge John Garrett Penn said in similar speeches to the three during their separate sentencings in the last two days.

The three Nigerians, Olatunji Mosuro, Francis Sheen and Oliyinka Sobomowa, were among six persons convicted May 22 of operating a heroin distribution ring that centered on a 54-year-old District man, Eddie Adair, and worked out of his Adair's Motel at 11th and U streets NW.

According to testimony in the two-month trial, Adair, whom prosecutors describe as being a middle-level drug distributor, obtained much of the heroin he sold from Mosuro, who worked with the other Nigerians.

Assistant U.S. Attorney William J. O'Malley Jr., who with Darryl W. Jackson prosecuted the case, said in court yesterday that Mosuro had been part of the Odetayu drug organization since at least 1984, and had been supplying Adair since then.

The Odetayu network is composed of Nigerians who import primarily Pakistani heroin into this country through Lagos, Nigeria, and The Hague, the Netherlands, O'Malley said. The drugs were regularly smuggled into the country in African artifacts brought in by couriers, and according to testimony, Sobomowa used that method to import heroin from Lagos last September, during the time he and others were being investigated by members of the Presidential Drug Task Force.

U.S. Attorney Joseph E. diGenova has said that at least two-thirds of all the heroin sold in the District is supplied by Nigerian nationals. More than two dozen Nigerians have been convicted here of drug trafficking in the past two years, but the recent convictions reflect the first time that Nigerians have been convicted of bringing the heroin into the United States.

O'Malley said in court that the involvement of Nigerian nationals in drug trafficking has continued despite the imposition by the Nigerian government of sentences ranging up to execution. He stressed that there was no evidence of involvement in the current case by the present Nigerian government.

During his sentencing Tuesday, Sheen, of 11342 Evans Trail Rd., Beltsville, said drugs were not part of the traditional Nigerian culture and that when he tried drugs, in what he termed a "status-seeking gambit," he was overtaken by "unseen and elusive forces" that were "unleashed within me."

Penn also sentenced Sheen to a one-to-four-year term for unlawful use of a telephone in furtherance of drug distribution.

Penn said he would recommend that Sheen be deported when he has completed his term and that Sheen not be allowed to reenter the United States.

Sobamowo, 38, of 7005 Highview Ter., Hyattsville, gave a long, rambling statement during his sentencing Tuesday in which he said he had been in the United States for 14 years and had "never distributed or imported narcotics."

Mosuro, who along with Adair and Sheen sat stoically throughout the trial dressed in heavy overcoats, sobbed loudly as he was brought before Penn yesterday.

"I beg you to give me another chance," said Mosuro, 40, of 8020 14th Ave., Hyattsville.

"I am just a cabdriver . . . . I have never seen drugs in my life," Mosuro said, as his wife Margaret, also sobbing, doubled over to the floor in the audience. "I beg your honor, I beg your honor," Mosuro said.

Mosuro, who was sentenced to two to eight more years on other charges, is serving an 18-month sentence for biting a federal officer after an early court hearing in the drug case.

Adair is expected to be sentenced next week.