Chief Abscam prosecutor Thomas P. Puccio threw Sen. Harrison A. Williams Jr.'s videotaped words back at him today, ridiculing the senator's claim that he didn't tell a phony Arab shiek he would try to get government contracts for a titanimun mine.

Alleged promises about government contracts are a key part of the bribery and conspiracy charges against the New Jersey Democrat. Puccio jabbed his finger constantly at Williams as he grilled him in a sarcastic tone about his taped statements and his thinking at the time.

The senator said government contracts were "the last thing on my mind" when he attended a June 28, 1979, meeting with the undercover FBI agent posing as the sheik. Minutes earlier undercover informer Melvin Weinberg had urged him to boast of his influence and to guarantee that he would help get the contracts.

The defense claims that Weinberg "put words in his mouth." Though the senator testified earlier that he had boasted of his influence, he said he ignored the suggestion that he promise to help get contracts. "My mind would not accept it," Williams told Puccio.

Puccio then replayed the videotape that showed the senator saying, "No problem . . . . It will come to pass," when undercover agent Anthony Amoroso suggested that the senator could use his position to help with contracts. Thursday, Williams told his attorney, George J. Koelzer, he had "nothing particularily" in mind when he said that. g

But today in a heated exchange with Puccio he said the statement was "a complete exaggeration . . . that adds up to nothing." He was simply trying to impress the sheik, he said.

"Are you telling us that as a United States senator you sat there in that room and said things that added up to nothing?" Puccio asked incredulously.

"I did," Willams said firmly.

"You were marching to the beat of Mr. Weinberghs drum?"

". . . Not in an area that I thought was important and vital," the senator responded, in an apparent reference to government contracts.

Puccio also attacked the senator's claim that he told the truth to FBI agents when questioned about the titanium mining venture early last year. He belittled Willams' statement that he had no personal stake in the mine. And he got the senator to agree that on a Jan. 15. 1980, videotape he pledged to aid the sheik's immigration problems after he'd been offered a bribe.

Earlier in the day Williams completed several hours of questioning by Koelzer. He said he refused the sheik's offer of money and had tried to explain that "in our country the public official does not accept money for anything he might do in connection with his public position."

Asked why he didn't walk out of the meeting at that point, the senator said he had been reminded that American companies often had to pay bribes to do business overseas, especially in the Middle East. "He impressed me as bringing his country's custom with him. What was done over there he has learned."

Keolzer's lengthy examination of his client was clearly intended to take the sting out of Puccio's questions about incriminating statements on the tapes. But the practice was so repetitious that U.S. District Court Judge George C. Pratt warned Koelzer privately Thursday that the jury might find the senator's testimony artificial and rehearsed.

At a sidebar conference out of the hearing of the jury and courtroom spectators, Pratt said, "You may convince the jury of exactly the contrary of what the witness is saying, simply because he is saying it so often. And it may become in their view very artificial and very rehearsed."

Pratt said he made the comments because he wanted Willams to get a fair trial. Koelzer replied that he knew the tactic was a risk. "Perhaps it is an audacious approach, and it is something that has to be done because the tape is there," he said.