Benjamin Greenberg, New Jersey roofer appeared yesterday before a grand jury believed to be investigating events leading up to the declaration of a mistrial in the first political curruption trial of nos suspended Gov. Marvin Mandel.

Greenberg, ordered Monday to testify or go to jail, left the grand jury room several times during his two-hour appearance to confer with his attorney about the questions he was reing asked.

When he left the courthouse, Greenberg said repeatedly that whatever he told the grand jury "doesn't have anything to do with Mandel."

Greenberg's attorney, James T. Vernile, said, "as far as we can see, there is no connection with the Mandel case."

Vernile had argued Monday that prosecutors should not force Greenberg to talk because their information about him was gleaned from allegedly illegal electronic surveillance. The judge disagreed and also refused requests that prosecutors turn over transcripts of conversations between Greenberg and Charles E. Neiswender, of Cinnaminson, N.J.

Neiswender was convicted of offering to fix the Mandel trial, but said during his trial that he was acting as an intermediary for someone else, who remains unknown.

Neiswender has appealed his conviction. His attorney refused to say whether the grandjury has asked Neiswender to testify.

A Baltimore furniture dealer, Gutman Kolodner, also testified before the grand jury yesterday. Kolodner's wife said the Walter E. Weikers, a second man convicted of tampering with the Mandel jury, has worked in her husband's furniture store since Weikers was released from jail Sept. 1. Weikers served 17 months of a two year sentence for offering $10,000 to one of the Mandel jurors.