Peter Bessell, a prosecution witness in the murder plot case against Jeremy Thorpe, tonight said that the former Liberal Party leader had been part of an attempt to defraud a healty Liberal benefactor of $500,000.

Bessell said he had suggested to Bahamas-based businessman Jack Hayward that a $500,000 bribe would facilitate a property deal.

"It was not entirely of my own devising," said Bessell, under cross-examination by Thrope's lawyer, Sir David Napley. "I am telling the court that Mr. Thorpe was party with me to endeavoring to perpetrate a fraud on Mr. Hayward."

The magistrates are sitting to decide whether Thorpe, 49, and three other men should stand trial in connection with a plot to murder Thorpe's alleged homosexual lover.

Bessell, a former Liberal member of Parliament, alleged that in 1973 Thorpe had joined him in devising the plan, which, if carried out, would have defrauded Hayward.

The transaction involved an attempt by Bessell to sell some property in the United States for Hayward. Bessell would have received about $1 million commission on the sale.

Bessell, 58, was flown from his present home in Oceanside, Calif. to testify in the case, and was given immunity from prosecution.

Earlier today, during grueling cross-examination by Napley, Bessell was accused of having said-on separate occasions-that he was an American spy and a bisexual, but he denied he was either.