A Bethesda chauffeur took the witness stand today and accused his son's father-in-law. Walter Weikers, of offering him a $10,000 bribe to fix the outcome of the political corruption trial of Maryland Gov. Marvin Mandel.

Oscar Sislen, a juror in the Mandel trial who was excused when he reported the alleged bribe attempt to the presiding judge stuck to his story during a hammering cross examination by Weikers defense attorney who repeatedly suggested that Sislen had solicited the bribe offer.

A mistrial was declared in the Mandel case after a television news bulletin about the Sislen bribe attempt coupled with news of another alleged attempt of fix the trial was overheard by several Mandal jurors who were watching the television.

Sislen, who occasionally contradicted himself and had trouble remembering Weikers' name testified that at a prearranged meeting off a cloverleaf at the Baltimore Beltway and 195. Weikers "asked me how would I like to make $10,000?"

"I said for what . . . He said to hold down the jury in the Mandel case . . . to get a hung jury," Sislen testified.

But Sislen also conceded under cross examination that he had complained to Weikers at their first meeting about how much money he was losing while serving as a juror. In addition, Sislen confirmed that he initiated the next contract between the two men when he called Weikers a week later to discuss the alleged bribe. The telephone call by Sislen was made at the request of the prosecutors, according to testimony.

Sislen was the first prosecution withness as testimony began today in the trial of Weikers, who is the stepfather of Sislen's daughter-in-law. During his testimony, the rotund moustachioed chauffeur frequently glanced down from the witness stand at the 67-year old furniture salesman against whom he was testifying. Weilkers glanced up at Sislen just as often, but their eyes never seemed to meet.

Behind them in the courtroom sat Weikers' wife, two daughter, his son and his son-in-law. A short distance away from them was Samuel (Buddy) Sislen. Sislen's son and Weikers' son-in-law. It could not be learned today whether Weikers' stepdaughter, Bonnie Sass Sislen was present in the courtroom.

In his testimony Sislen said that telling the presiding judge in the Mandel case about the bribe offer "was a hard thing to do. It's still a hard thing to do," said Sislen, his eyes darting across the row of relatives in the spectator section of the court.

"But . . . I just had to tell him."

Later Sislen said that he was trying to help Weikers, first by going to the authorities with his story and then by allowing postal inspectors to monitor and tape-record his conversations with Weikers. This comment drew small sounds of disbelief from the area of benches where the Weikers family sat.

However, when Dorothy Sislen took the stand immediately after her husband, she reiterated his sentiment. As defense attorney Harold I. Glaser asked her if she wanted to see Weikers convicted, she said, "We never wished Mr. Weikers any kind of harm and we never have . . ."

She added that the Sislen had hoped Weikers would "take steps to protect himself" by leading prosecutors to the original instigator of the bribe attempt.

Sislen testified, that, after he told his story to the judge, prosecutors had asked him to arrange another meeting with Weilkers - a meeting that would be monitored and tape-recorded by federal agents - "to see if I could get him to tell me where the money was coming from."

According to court documents filed after the Mandel case was aborted, prosecutors believed that an individual they call "the shark" set in motion both the alleged bribe attmept by Weikers and an earlier attempt to fix the trial allegedly made by Charles Edward Neiswender, of Cinnaminson, N.J.

The officially aranged meeting between Weikers and Sislen took place in the mid-afternoon of Nov. 30, inside the Fradkin Bros. Furniture Store in suburban Baltimore where Weikers is a salesman. During the meeting, "(Weikers) kept repeating that he would guarantee the delivery of the goods, as he put it," Sislen said.

According to Sislen, Weikers also said that he had approached his relatives with the offer because Sislen was "the only Jewish boy" on the jury.

After he emerged from the meeting inside the store, Sislen testfied that he was told by federal agents that the store's fluorescent lighting had interfered with the recording of the conversation. The agents, Sislen said, asked him to bring Weikers to his car on some pretext, so a recorder in the car could catch Weiker's words clerly.

Mrs. Sislen, who had been waiting in the car while her hushand and Weikers talked inside the store, testified that when her hushand brought Weikers to the cars, Weikers told both of them "that he would have to contact someone; that we could have the goods the next day; that we could have it up front."

Tapes of that meeting and the earlier phone call from Sislen to Weikers during which the meeting was arranged are expected to be played to the jury Thursday.

During his opening statement, and repeatedly during his cross-examinations of Sislen and his wife, defense attorney Glaser contended that Sislen himself solicited the bribe.

By telling his story to prsecutors and agreeing to let them attach a recording device to him for the meeting with Weikers, "Mrs. Sislen was just trying to get himself off the hook," Glaser said.

"Mr. Sislen had spoken to other people about getting money for a verdict of not guilty," the defense attorney told the jury before testimony began today.

In addition, during his cross-examination of Sislen, Glaser forced the white-haired chauffer to admit that, during his initial twilight conversation with Weikers by the highway, Sislen complained about how much the trial was costing him in lost income and travel expenses.

Glaser also pointed out repeatedly that, after that roadside meeting, Weikers did not contact Sislen again, and that the next contact between teh two men, a week later, was initiated by Sislen himself.

"From the time he offered you a $10,000 bribe he never called you back?" asked Glaser.

"I would say it was unusual," Sislen responded.

"The reason it was unusual is because he never offered you a bribe," Glaser shot back.

"No," Sislen answered.

Later, Glaser introduced Sislen's bank records for 1976 into evidence, to show that the Sislen's checking account had been slowly depleted during the two months that Sislen sat on the Mandel jury. Jurors in federal court are paid $20 a day; Sislen testified that he had been earning between $200 and $300 a week before the

However, despite elicting occasional discrepancies between Sislen's testimony and that of his wife, Glaser was not able to shake the core of both their stories: that Weikers first called Sislen on Nov. 18, first made the bribe offer at the Nov. 23 roadside meeting, and reiterated at the meeting at the furniture store on Nov. 30 that the money to pay the bribe was readily avaible.

Weikers was arrested by postal inspectors immediately after that Nov. 30 meeting.

In convicted, he could be sentenced to a maxium $15,000 fine and five years in jail.