A defense effort to show that Sen. Harrison A. Williams Jr. (D-N.J.), on trial here in an Abscam bribery case, couldn't have influenced government contracts for titanium almost backfired today when prosecutor Thomas Puccio said that the last government contract for the strategic titanium stockpile had been awarded on the recommendations of Sen. Howard W. Cannon (D-Nev.).

Puccio's surprise disclosure was immediately challenged by defense attorneys, and U.S. District Court Judge George C. Pratt told the jury at Williams' trial that the remarks about Cannon were not in evidence.

Defense attorneys complained after today's court session, however, that Puccio's comments couldn't be ignored.

Williams and co-defendant Alexander Feinberg are charged with conspiracy and bribery in a scheme whereby the senator allegedly agreed to get government contracts for titanium in return for a promised $100 million loan for a titanium mining venture in which he would hold a hidden interest.

Puccio's reference to Cannon came during his cross-examination of Harold C. Petrowitz, an American University law professor who was testifying as an expert witness for the defense on government contracts.

In a key June 28, 1979, videotape introduced by the government last week, Williams is shown promising undercover FBI agents that government contracts would be no problem and that he would take the matter to the president. Petrowitz said today that "nothing I have seen or know about would indicate that Sen. Williams has any direct say in goverment procurement or stockpiling."

Puccio then asked if Petrowitz was aware that the last government stockpile contract for titanium had gone in the 1970s to a Henderson, Nev., company on the recommendation of Cannon. He also asked whether he knew that "in return for the award," executive branch officials had urged Cannon to support othe legislation.

Pucio said after today's session that he based his questions on a 1979 New York Times article. "I'm not saying Sen. Cannon did anything wrong," he said.

The article was based on General Services Administration reports that charged mismanagement of the nation'smineral stockpiles. Cannon's intervention on behalf of a failing titanium mine in his home state was cited as an example of such mismanagement. Cannon could not be reached today for comment.

During the rest of the day, Williams' attorney, George J. Koelzer, called a series of witnesses to establish that the senator's friends had sought legitimate financing for the titanium venture. Koelzer seemed to be trying to lay the basis for the defense that Williams and Feinberg were entrapped by government agents who required the promise of government contracts in return for the loan