D.C. businessman Hugh D. Mason III was sentenced to six months in federal prison and fined $5,000 yesterday for conspiring to bribe an official of the city's Minority Business Opportunity Commission.

U.S. District Judge Stanley Sporkin also ordered Mason to serve three years' probation, after the prison term, on a separate charge of aiding and abetting the paying of gratuities to a D.C. lottery board executive.

Sporkin praised the continuing probe of public corruption by the U.S attorney's office, saying, "There is no kind of work a prosecutor is committed to do that can be more important to a community than ferreting out corruption," Sporkin said, addressing Mason during the sentencing hearing.

"Corruption in government must be eradicated," Sporkin said, adding that those convicted of public corruption must be "dealt with strictly."

The judge said he believed Mason's illegal activities could have "mushroomed to the point where they would have had a serious impact on local government."

Mason, 43, would have received a much "stiffer sentence" if he had not been cooperating with prosecutors since his guilty pleas on Jan. 6, Sporkin said. Mason has appeared before a federal grand jury investigating city contracting practices, and Assistant U.S. Attorney David S. Eisenberg said Mason had provided "very critical and important information."

Two letters giving details of Mason's cooperation have been sealed by the court, as was the agreement that resulted in his guilty pleas. However, Mason's attorney, Nicholas Balland, said in court that Mason has a continuing obligation to cooperate, which usually means that a person is expected to give additional grand jury or court testimony.

"I truly regret having gotten myself involved in this situation," Mason told Sporkin. Mason, who could have received seven years in prison and a fine of $20,000, stood quietly as the sentence was imposed; his wife choked back tears.

As part of his plea, Mason admitted he gave a commission official $200 to speed up the certification of a minority firm, a janitorial concern called Pace Setters Management Inc. Sources familiar with the case have identified the commission official as Frank S. Borris, a former deputy director. Borris has not been named in court papers or charged in the case.

Mason also admitted funneling $500 to former D.C. lottery board executive assistant Alexander Exum from Han Yong Cho, a D.C. businessman who was seeking a contract from the lottery board. Exum pleaded guilty in April 1986 to accepting a total of $5,500 from Cho.