Charles Edward Neiswender, a self-described New Jersey "con man" offered to 'fix' the political corruption trial of Maryland Gov. Marvin Mandel for $20,000 a key witness in Neiswender's obstruction of justice trial testified today.

The offer was made to a man Neiswender believed to be associated with Mandel's defense lawyer but who was, in fact, an undercover U.S. Postal Inspector, Brooks E.Todd.

Todd testified today Neiswender told him he was acting on behalf of a juror who was willing to throw the case for a price. Neiswender also said he was acting as an intermediary for someone else who was "in politics a little bit" in Maryland.

Neiswender, who called himself a "conman" in an interview with The Washington Post in December, is the second man to stand trial for allegedly tampering with the jury in the Mandel trial. Walter Weikers, a Baltimore furniture salesman, was convicted of obstruction of justice earlier this month for a jury-tampering attempt. There has been no evidence presented that the two incidents were related.

News reports of the jury tampering allegations were heard by jurors in the Mandel trial prompting U.S. District Judge John H. Pratt to declare a mistrial Dec. 7. The governor and five codefendants are scheduled to be retried in April.

Government agent became involved in the case after Mandel's lawyer, Arnold M. Weiner, told them he had been contacted about the jury-tampering offer.

Tood also testified that toward the end of a series of call and meetings that took place over a two-week span last Fall, Neiswender threatened that the juror might hold out for a guilty verdict if the payment was not made.

In addition to the testimony of Todd, the jurors on the case also heard tape recordings today of the conversations between Todd and Neiswender - who was using the alias of Lee Anderson - during which Neiswender allegedly solicited the bribe and made the threat.

However, at the close of the prosecution's brief case this afternoon, Neiswender's defense attorney asked presiding Judge Frank A. Kaufman to acquit the 52-year-old defendant, since the prosecution had not established that Neiswender ever had contact with a juror. Soliciting a bribe from a defense attorney they contended, does not constitute obstruction of justice under federal law.

Referring to the tapes of Neiswender's conversations with Todd and Weiner, the defense attorneys argued that "all these conversations stand for is an offer by (Neiswender) to 'fix' for a fee, a pending judicial proceeding . . .

"There is no evidence of any overt act on the part of this defendant which would tend to show an actual endeavor to obstruct the proceeding in the United States versus Mandel," defense attorneys J. Frederick Motz and Charles M. Kerr argued.

In rebuttal, Assistant U.S. Attorney Barnet D. Skolnik argued that by the act of approaching an attorney in the case, Neiswender had obstructed justice."No attorney can discharge his duty influenced by the knowledge that the case is fixed," Skolnik said.

Judge Kaufman then refused to grant the motion for acquittal.

Earlier in the day, as the prosecution presented its case - three witnesses and 90 minutes of tape recordings - the jury heard a recording of Neiswender telling Todd that he was acting as intermediary both for a juror and for a third party who was "in politics a little bit" in the Baltimore area.

"They (the juror and the unnamed intermediary) are, I guess they're just buddies and they drew the whole thing together," Neiswender told Todd in an Oct. 4 phone call.

Neiswender added in two other taped conversations that he was being paid a $2,000 fee - "two big ones" - for his efforts as a go between.

According to testimony today, the bribe solicitation began on Sept. 21, when Neiswender called Weiner's office, identifying himself as Lee Anderson, and left a message that he would call Weiner back.

In his first phone conversation with 'Anderson' two days later, Weiner testified, "he said . . . his man could guarantee that Gov. Mandel would be acquitted.

". . . He suggested that I relay his message to Gov. Mandel . . . and if the appropriate financial arrangements were made he was prepared to do what he was offering."

Immediately after the call, Weiner said, he contacted the U.S. Attorney's office, and agreed with prosecutors to have his next talk with 'Anderson' recorded and to have postal inspector Todd, who had been working on the Mandel case pose as an attorney in Weiner's firm.