A 35-year-old Glen Burnie woman was convicted today of lying to a federal grand jury investigating her alleged attempt to buy secret information from a member of a 1975 panel investigating political corruption allegations against former Maryland governor Marvin Mandel.

The jury of nine men and three women retired to deliberate Thursday and considered the case for a total of 12 hours before finding Donna B. Brown guilty of a single perjury charge.

Brown, who had joked freely with reporters and friends during the six day trial in U.S. District Court here, sat calmly next to her husband Robert when the verdict was read, but broke down and cried on her mother's shoulder as soon as she left the courtroom.

The heart of the perjury case was the series of conversations Brown had in 1975 with her best friend, Diane Lawrence, who was a member of the grand jury investigating Mandel and his associates Harry W. Rodgers III, William A. Rodgers, W. Dale Hess, Irvin Kovens and Ernest N. Cory.

Unknown to Brown, the FBI recorded several of her conversations with Lawrence in which Brown talked of offering $1 million to Lawrence for the information. The jury spent most of its deliberation time listening to the eight hours of tape recordings a second time.

Brown testified in her own defense last week that the alleged scheme was a "joke" that she failed to recall when she appeared before a 1978 grand jury and was questioned about it.

"There wasn't any reason to tell Diane it was hoax," Brown said. "She knew it was . . .she didn't question it for three long years. Perhaps I was guilty of bad judgement, but I didn't bribe anybody."

Judge Frank A. Kaufman set May 29 for sentencing. Brown could receive up to five years in prison and a $10,000 fine. She also faces another trial on a charge of attempting to influence a grand jury.

In several interviews last week, Harry Rodgers said he met with one of Brown's friends three times during 1975 to discuss what kind of grand jury information was available.

Rodgers said that when the talks turned to how much he was willing to pay for the information, he told the man - a Harford County contractor - he "wash't interested."

Rodgers was not called to testify in Brown's trial. But the contractor, Warren C. Eastburn Sr., testified that he repeatedly discussed the alleged "deal" with Brown's husband. Eastburn was given immunity from prosecution in exchange for his testimony.

The two Rodgers, Hess, Kovens, Correy and Mandel were convicted on political corruption charges in 1977, but that conviction was overturned last January by the 4th U.S. Corcuit Court of Appeals.

Brown's attorney, Harold I. Buchman, said today he would file a motion for a new trial.

Brown and Lawrence ended their longstanding friendship last summer. Brown said her "joke" did not contribute to their breakup.