Rep. John W. Jenrette Jr. (D-S.C.) took the witness stand in his own defense in federal court here yesterday and denied that he ever got a $50,000 cash bribe from an FBI agent posing as a representative of a phony Arab sheik.

Jenrette, 44, told the jury that he did draw up a $10,000 note payable to his codefendant, John R. Stowe, last Dec. 6, the same day that secret FBI videotabes showed Stowe accepting $50,000 in cash from an FBI undercover agent who was part of the bureau's Abscam "sting."

Jenrette, visibly nervous during two hours of testimony yesterday, told the jury that he kept the $10,000 locked up in his congressional office in South Carolina until late last January. At that point, he testified, he used the cash to repay his wife's parents, who had invested in a failing real estate venture in South Carolina in which Jenrette was a partner.

Jenrette and Stowe, a former Richmond businessman, are charged with conspiracy to accept payoffs in exchange for Jehrette's promise to introduce private immigration legislation for fictitious Arab sheiks.

FBI videotapes presented during their trial in U.S. District Court showed Jenrette and Stowe at a house on W Street in Northwest Washington on Dec. 4, 1979, where they met with an FBI undercover agent and an informer and discussed whether Jenrette could come through with the private bill in exchange for a total of $100,000.

Jenrette told the jury yesterday that he was "intoxicated" and "scared" during that meeting and that he later thought "I was involved with something I couldn't handle." The defense contends that Jenrette believed that he had gotten mixed up with organizing crime figures.

Jenrette said that 10 days before he went to the meeting at the W Street house he had received a demand from a bank for $51,524 that was due on his South Carolina real estate project, called Oristo Properties, a condominium resort about 40 miles south of Charleston.

Jenrette, under questioning from defense lawyer Kenneth Michael Robinson, said he had more than $300,000 in obligations stemming from the project.

"I could have saved Oristo with $50,000 or even less than $50,000." Jenrette testified in connection with the bank's demand for money.

"Did you ever get that money, the $50,000?" Robinson asked him.

"No sir," Jenrette testified.

"Did you ever pay that money at any time?" Robinson asked Jenrette later in his testimony.

"I haven't paid it," Jenrette said.

The defense contends that Jenrette's frequent bouts with alcoholism and his financial troubles made him a vulnerable target for the FBI undercover agents and their Abscam "sting."

Yesterday, during his testimony, Jenrette reluctantly described "several offices in the Capitol where there are alcoholic beverages available." When members of his staff cleared the liquor out of his office and replaced it with diet soda, Jenrette testified, he would retreat to those unidentified offices for a drink.

Jenrette also testified yesterday that he has been the subject of numerous criminal investigations, which began, he said, in 1974, when he won South Carolina's 6th Congressional District seat. Jenrette maintains that his Republican opponent's former campaign manager, who by then was the U.S. attorney, marshaled a series of politically motivated investigations against him involving another South Carolina real estate project in which Jenrette had been involved.

Jenrette said he has also been under investigation concerning employe kickbacks, misuse of the telephone, misuse of postage stamps from the congressional stamp office, illegal campaign contributions and alleged connections to drug smuggling. None of the cases ever resulted in indictments, he testified.

Jenrette is expected to continue his testimony Monday.