The codefendant in Sen. Harrison A. Williams' Abscam trial acknowledged under cross-examination today that he continued to seek financing for a titanium mine and other ventures from undercover FBI agents posing as representatives of a fictitious Arab sheik despite their constant statements they wanted to make political payoffs.

Alexander Feinberg, 72, a longtime friend of the New Jersey senator, told prosecutor Thomas Puccio that he did hesitate several times when undercover informant Melvin Weinberg talked about making payoffs.

But Feinberg said he still believed he could get legitimate loans for the mine and other business deals he discussed during 1979 in meetings and calls secretly recorded by the FBI.

Feinberg and Williams, the 61-year-old former chairman of the Senate Labor and Human Resources Committee, are charged with bribery and conspiracy for allegedly trying to trade the Democratic senator's influence in getting government contracts for titanium in return for a $100 million loan to develop the mine. Williams allegedly held a hidden 18 percent interest in the mine.

During lengthy and often barbed cross-examination, Puccio challenged Feinberg's explanations of his conduct. Several times the prosecutor asked Feinberg why he continued to deal with the apparently corrupt Arab representatives.

For example, in one exchange about another deal, Puccio asked Feinberg: "When Mr. Weinberg talked about something blatantly illegal, why didn't you walk away from him?"

Feinberg replied, "I felt an obligation to try to help out my clients."

Later, Puccio attacked Feinberg's contention that he was merely trying to "placate and appease" Weinberg when he made incriminating statements about the senator's effort to get government contracts for the mine. At one point Puccio asked, "Did it ever occur to you to walk away from this whole thing, Mr. Feinberg, and stop placating people?"

The defendant answered that he had considered it on several occasions, but "when weighing the destruction of all the effort [on the mine deal] . . . I hoped that I could legitimately bring this to a successful conclusion."

By the end of the day Feinberg had talked so often of placating Weinberg that he answered one question by saying, "I'm in the sphere of placation there."

The prosecutor also tried to focus the jury's attention on a June 19, 1979, meeting in Williams' Senate office in Washington where Feinberg and Angelo Errichetti, the mayor of Camden, N.J., told the senator he would have to tell the "sheik" he could get government contracts.

"Is it fair to say there was a reason for a United States senator to go into a room and say he could get government contracts?" Puccio asked.

When Feinberg didn't respond immediately, Puccio pressed: "Did you say he shouldn't do that?" When Feinberg said he hadn't, Puccio asked why not and the defendant replied, "I wanteds to placate all these people."

"You wanted to placate them so you could make some money?"

"So the project could be successful," Feinberg responded.

That exchange was repeated twice in heated terms, and Feinberg never did agree to the prosecutor's characterization.

Earlier, Feinberg acknowledged he had lied to FBI agents when first questioned in February, 1980, about Williams' share in the mine. "They asked you the $64 question: 'Who has the other 18 percent?" Puccio said.

Feinberg replied, "In response, instinctively, intuitively, in a protective manner, I denied. . . .

"Instinctively, I had a protective interest toward Sen. Williams."

Asked why he was trying to protect the senator, he said, "I don't know."

Feinberg also denied that he was suspicious that Joseph Silvestri might be cooperating with the FBI when he called Feinberg the day the scandal broke last year. In that conversation, recorded by the FBI with Silvestri's approval, Feinberg insisted that the mining venture was legitimate and that the senator was "an honorable man."

In grilling Feinberg about several other business ventures he discussed with Weinberg, Puccio tried to show the defendant was no stranger to hidden business deals. For instance, after discussing a "finder's fee" in one proposal, the prosecutor asked if the defendant wasn't really just calling a bribe a fee. Feinberg denied that.