Sen. Harrison A. Williams Jr., his political fate on the line, pleaded for five lonely hours yesterday for his colleagues to reject "the preposterous notion" that he be expelled from their number.

"More than 23 years ago, I stood proudly in these chambers to take my oath, an oath I have never violated," the New Jersey Democrat told the packed Senate at the beginning of the afternoon.

For the rest of the day, Williams tried to shift the debate away from his own activities to those of the government in the Abscam investigation, which resulted in his conviction on bribery and conspiracy charges.

"If the Abscam operation is to be understood in its totality, not only my conduct but the government's conduct must be considered," said Williams, only the third senator in history convicted of a felony while in office.

Williams, flanked by two attorneys, stood at his seat in the second row near the center of the chamber. For the most part, he read from a prepared text, his left hand thrust deep in his pocket.

Waiving the immunity that protects words uttered in the chamber, Williams spoke in a slow, low-key, almost unemotional tone--the kind of friendly and unassuming voice one might use in a living-room conversation.

But his words were full of bitterness and inner agony. "My wife and I have been under some ordeal, I tell you, for over two years," he said. It has been "an Orwellian nightmare" and a "lonely fight."

The day his name was first linked to Abscam, scores of reporters--"equal to the number covering a presidential inauguration," he said--camped out in his Georgetown neighborhood.

It was like a "hue and cry in Old England," when "people hear the hue and cry and join the chase to get the criminal," he said. "With the press and all the media, it was a hue and cry, and all the other media followed."

Of the 1,753 people who have served in the Senate, only 15 have been expelled--all for disloyalty or treason. Fourteen were Confederate sympathizers; the fifteenth, William Blount, was expelled for trying to incite an Indian war in 1797.

Williams' 99 peers know this. And yesterday their eyes were riveted on him as his often-rambling presentation began. A few, such as Charles McC. Mathias Jr. (R-Md.), took notes on yellow legal pads. Others, such as Edward M. Kennedy (D-Mass.), slipped off the floor occasionally. Most sat slumped in their chairs, with chins in hands.

Williams, 62, was long a powerful insider in the chamber; a quiet, unassuming former chairman of the Labor and Human Resources Committee, and part of the Democratic liberal wing.

From the beginning, his case has been a messy melodrama, full of pathos, dashed hopes and political tragedy. It was no less yesterday.

"I feel for you, but I can't apologize," he told his fellow senators, adding that the fight against expulsion was one he had to undertake. "I say to you, 'Try to put yourself in my situation.' "

As he said this, Williams, dressed in a black suit, peered over his half-glasses at Vice President Bush, who was presiding for the second full day.

Williams' wife, Jeanette, a former Senate aide who helped him overcome alcoholism a decade ago, looked on from the gallery to his right.

Later, she told a press conference that the Abscam investigation of her husband was "like raping Alice in Wonderland."

During his presentation, Williams used several large charts to illustrate his points. One quoted Irvin B. Nathan, a former assistant U.S. attorney general, as saying that public officials "have to be concerned that the people they may be dealing with are undercover agents and matters may ultimately be on tapes and may be presented in courts."

If that is the way of the future, it is the way of the future written about by George Orwell in his novel "1984," Williams said.

Six congressmen also were convicted in Abscam, five on bribery and conspiracy charges and the sixth for conspiracy and accepting an illegal gratuity. One was expelled from the House and the others either resigned or were defeated for re-election.

A federal jury in May convicted Williams of agreeing to use his office for a hidden share in a mining venture that was to have been financed by a $100 million loan from an undercover agent posing as an Arab sheik. He received a three-year prison sentence.

Williams claimed yesterday that the case against him was created "out of nothing" by "renegade individuals" in the FBI and the Justice Department.

He said he was the victim of an overzealous FBI inquiry in which "this Abscam net was so crudely wrapped around me," and he presented a number of items that he claimed represented new evidence in the case. One was a Nov. 27, 1979, internal government memorandum in which Justice Department officials said it would be "necessary to recontact" Williams "to obtain an overt action on his part"--because, the senator said, they had been unable to catch him in wrongdoing.

He also presented an analysis of videotaped meetings with undercover agents. The analysis was made by Roger Shuy, a Georgetown University linguist, who maintained that Williams' words on the tapes did not convey his true intentions.

At the end of the day, Senate Minority Whip Alan Cranston (D-Calif.), as he has done before, said an investigation is needed to determine the extent of government misconduct in the case. He said Williams deserves censure, not expulsion.

Earlier, Majority Leader Howard H. Baker Jr. had said he would oppose Cranston's move, and Sen. Malcolm Wallop (R-Wyo.), chairman of the Ethics Committee, which voted 6 to 0 last summer to expel Williams, said he doubted that a censure move could pass.

"I'm still confident the committee position will hold sway," Wallop said.

The debate continues Monday, with a vote expected Tuesday on expulsion, which requires two-thirds of those present and voting.

Said Williams: "What the Senate of the United States does, I will accept, I will respect."