Testifying for the defense at the trial of Sen. Harrison A. Williams Jr. (D-N.J.), a former New Jersey Casino Commission official testified today that the senator had never tried to use his influence on behalf of a company for which Williams' wife was a paid consultant.

Joseph A. Fusco, then head of licensing for the comission, told the jury at Williams' Abscam bribery trial that he considered the application to rebuild Atlantic City's Ritz Hotel strictly on the merits, without any outside interference. "We did not respond to outside influences," he said.

Fusco was called to rebut a damaging Oct. 7, 1979, videotape in which Williams boasted to undercover FBI agents that he had influenced the commission's decision on the Ritz and saved its backers $30 million.

In that same tape, made at the Plaza Hotel in New York, Williams also discussed getting a $1 million finder's fee for arranging financing for the Ritz through the Arab "sheik" the government agents pretended to represent.

Williams' wife, Jeanette, who has been attending the trial each day, was a member of the board of directors and later a paid consultant to Hardwicke Companies Inc., the majority investor in the Ritz proposal. Though preliminary permission was granted in May 1979 to rebuild the hotel, the project has never been completed.

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

Though Williams' action concerning the casino venture are not mentioned in the indictment, they are considered important evidence in the trial because they may help the jury determine whether Williams was predisposed to accept the alleged bribe in the titanium venture.

Defense attorneys objected when the government tried to introduce the Oct. 7 videotape in which Williams and Feinberg discuss the Ritz.But U.S. District Court Judge George C. Pratt said he would allow it because he expected the defense to claim that the undercover agents entrapped the defendants, and that the tape was relevant in showing similar conduct.

On that tape, Williams explained that he had "handled" Casino Commission Chairman Joseph Lordi, while Feinberg said he had influenced Vice Chairman Kenneth MacDonald. "The two of us. There's no two ways about it. We did it," Williams said.

Feinberg added: "MacDonald and Lordi happened to talk . . . obviously, those two sold the others on the commission the bill of goods."

In one part of the tape, the undercover agents asked Williams if Lordi had promised to take care of the Ritz vote.

"Well, no," Williams said, "he didn't tell me that. You know, he doesn't talk that way."

Feinberg: "You known they don't talk . . . ."

Williams: " . . . He'd work on it."

Feinberg: "It's another way of saying it."

Lordi was not called to testify today. He has publicly denied previously that Williams ever tried to influence him on the Ritz decision.

MacDonald resigned from the commission last year after it was reported that he and Angelo Errichetti, mayor of Camden, N.J., allegedly accepted a $100,000 bribe from the Abscam agents for influencing a casino license.

In other testimony today, Williams' administrative assistant, Walter Ramsey, said he prepared the senator's yearly financial disclosure statements and that Williams never tried to hide any of his interests.

Defense attorney George Koelzer has tried to show that the titanium stock didn't have to be disclosed because the loan was never received and the stock was worthless.