The Senate Ethics Committee yesterday recommended unanimously that Sen. Harrison A. Williams Jr. (D-N.J.) be the first senator to be expelled since the Civil War, but asked the Senate to delay its decision pending Williams' appeal of his Abscam conviction.

Williams immediately declared himself gratified by the committee's plea to the Senate, and repeated his determination to fight expulsion. "I am going to advance every opportunity that is before me to show clearly my innocence. This is a significant step in furtherance of my opportunity," he said when told of the outcome of the seven-hour committee session.

Not since 1862 has the Senate expelled a member, and it is clear that a majority of the committee was reluctant to follow the advice of Special Counsel Robert Bennett to press for expulsion as soon as possible.

Instead, the committee resolution urges senators to take account of Williams' appeal and to take time to study the mass of documentation-- including the notorious Abscam videotapes -- before reaching a conclusion.

The committee, however, was unanimous in condemning Williams' conduct. Chairman Malcolm Wallop (R-Wyo.) announced that it found, "based on the evidence before it, that Sen. Williams' conduct was ethically repugnant to the point of warranting his expulsion from the United States Senate." No one had enjoyed voting for expulsion, said Wallop, but it had been a fair judgment.

Williams, 61, was convicted in May of nine charges of bribery and conspiracy for agreeing to trade his influence for a hidden share of a $100 million loan from an undercover FBI agent disguised as an Arab sheik.

He was the first incumbent senator to be found guilty of a criminal charge since 1905.

He has repeatedly rejected resignation and told other senators in a private letter at the beginning of the Ethics Committee hearings that they should consider the implications of the methods used in the Abscam case.

"When one member is subjected to the whims of a prosecution determined to make a case by any means necessary, then all members are equally jeopardized," he said.

Six members of the House were convicted in the Abscam case. One, Michael (Ozzie) Myers (D-Pa.), was expelled; two resigned, and the others were defeated when they ran for reelection.

In yesterday's climax to the Ethics Committee hearings, Williams' lawyer, Kenneth Feinberg, urged the members to consider the senator's pending appeal on which U.S. District Judge George Pratt is expected to rule in October.

Bennett, however, wanted the committee to recommend expulsion without adding its suggestion --which the Senate is free to ignore-- that senators should wait until after Pratt's ruling before deciding.

Each counsel spoke for about 90 minutes to the committee in closed session, and the members then spent more than four hours discussing the case before taking the vote that unanimously recommended expulsion. One staff source said the decision was reached more quickly than had been expected.

Wallop emerged at about 5 p.m. to read the agreed statement, which said, in part: "The Ethics Committee recognizes that the due process in Sen. Williams' case is still pending before Judge George Pratt and that matters in the due process, matters in litigation could arise which the full Senate might want to consider.

"Thus the Ethics Committee recommends that the full Senate proceed expeditiously toward final disposition of its resoltuion only when Judge Pratt has ruled in the aforementioned matter."

Williams, who was first elected to the senate in 1958, was told of the decision by Feinberg as he waited in his office. He showed little emotion as he once again condemned the FBI for "manufacturing a crime."

When Wallop was asked if he thought Williams should resign, he said: "That is a matter only Sen. Williams can come to grips with."

Williams said: "I certainly feel in my heart and I know in my heart I have not done anything that warrants resignation or expulsion from the U.S. Senate."

The committee resolution will be sent to the Senate within the next few weeks. But if members decide to accept the "wait and see" recommendation, a hearing on whether to make Williams the 16th senator to be removed, and the first since three supporters of the Confederacy were expelled in 1862, will not begin until October.