To hear Newt Gingrich's lawyer explain it, the former speaker and his estranged wife, Marianne, agreed to a divorce settlement yesterday because the whole sordid spectacle had begun to erode Newt's capability to yak for cash. The confidential agreement, reached outside Atlanta after 12 exhausting hours of court-ordered mediation, averts a trial that promised to be really public and really ugly.

It leaves Marianne Gingrich, 48, without a husband after 18 years, and while financial terms were not disclosed, she does retain some shred of dignity.

For Newt, it may be too late. "If your name gets impaired, then it impacts your ability to make money," Randy Evans, who has been Gingrich's business attorney since 1995, said yesterday.

In the last month, Capitol Hill chatter about Gingrich vs. Gingrich usually began the same way: "Six years?!?!"

For six years, Gingrich, 56, two-timed his wife with a blonded-up, French-horn-playing Agriculture Committee staffer. His thing with Callista Bisek, now 33, was going strong through the Gingrich Revolution of 1994 that turned the Congress over to Republican majorities. It kept up through the Republicans' "Contract With America," Gingrich's 10-point plan to turn America to the right values. It steamed along during his ascendancy to speaker, when he gestured toward his proud wife in the balcony and called her his "best friend and closest adviser," adding, "If I listened to her 20 percent more, I'd get in a lot less trouble."

On it played through 1996, when Marianne campaigned vigorously for her husband, beamed from his side and shook countless hands. It stood strong while Marianne underwent the trauma and disappointment of unsuccessful in-vitro fertilization. While Gingrich lambasted the president at every opportunity for lying about his affair with Monica Lewinsky, while he successfully orchestrated the first presidential impeachment in a century, he was committing adultery himself.

Not that his wife ever knew, she said, even though both she and Gingrich had talked frankly of trials in their marriage, even though Bisek's name surfaced publicly in a 1995 Vanity Fair profile of Gingrich. (The young Hill aide was mentioned coyly as "a favorite breakfast companion.") When Gingrich told Marianne he wanted a divorce last May, she described herself as "blindsided" and "shocked."

Her friend, Debbie Dingell, the wife of Rep. John D. Dingell (D-Mich.) described Marianne yesterday as "broken up about" the dissolution of her 18-year marriage. "She is happy to have avoided a trial, but it's a sad day for everybody," said Dingell.

"It's not a sense of exhilaration," said Marianne Gingrich's divorce attorney, John Mayoue. "There is some sense of relief that this battle which she never sought and did not initiate is behind her."

Gingrich's attorney said he would not permit his client to discuss the divorce until after a Cobb County, Ga., judge approves the settlement early next year. "Any time you are dealing with emotional issues, it is very taxing," said Evans. "At the end there was a feeling of closure and relief that they can both move on with their lives."

Publicly, Democrats are sitting on their hands to keep from clapping over the Gingrich spectacle. Privately, "I chortle every day," said a party leader in Atlanta earlier this week.

"It's the utter gall that takes your breath away," says a Democratic leadership aide. "He's married. He's having an affair with a junior staffer on the Hill, when he's king of the Hill."

Back in his 1978 congressional race, after he'd been fooling around some on his first wife, Jackie, Gingrich's campaign slogan was "Let Our Family Represent Your Family." In a leaflet, he argued that his opponent would have to separate her family to move to Washington and would have to hire a nanny to fulfill her maternal obligations. ("All I'll say," he said of those years, "is that I have led a human life.")

Gingrich loyalist Rich Galen, who used to run Gingrich's GOPAC, argues that the former speaker's adultery has no analogy with Clinton. "At the end of the day, it's not like [Bisek] was on his staff. It's not the same as having an intern in the executive office," says Galen. He points out that Gingrich did not lie about his affair under oath, as the president did, and adds that the former speaker always took pains to focus on Clinton's law-breaking, not the sex. (And that time Gingrich called Clinton a "misogynist" in a closed caucus meeting? Probably just more human life.)

Many of the speaker's former faithful don't want to be seen anywhere near him. Some Republican congressional members argued strenuously that the blowout bash next month to celebrate the fifth anniversary of the "Contract With America" be held without any invite to its chief architect. Gingrich then stepped aside.

Many other conservatives are harshly critical.

Writing in the New York Times, the Weekly Standard's David Brooks excoriated Gingrich for considering himself "a history-making Ubermensch." Noting that the former history professor had jotted a note to himself in 1992 in which he listed his primary mission as "advocate of civilization, definer of civilization, teacher of the rules of civilization and leader (possibly) of the civilizing forces," Brooks added: "Why should the leader of the civilizing forces (possibly) worry about anything as puny as a marriage vow?"

Said Arianna Huffington, a onetime admirer who soured on Gingrich in the last few years: "The right has completely lost any credibility in defining moral values. It's laughable."

Such language can get in the way of a guy's ability to give $50,000 speeches and continue to buy his girlfriend a Big Bertha golf club and a $450 bottle of wine, gifts Gingrich lavished on Bisek, who sings in the National Shrine choir. (Bisek did not return several phone calls seeking comment, but on her voice mail, she sounds like an alto.)

For friends of Marianne, the animus toward Gingrich is much more personal. Many a ladylike congressional wife interviewed for this article used unprintable epithets.

One friend recalls a gala Marianne Gingrich hosted a few years ago to benefit the Children's Inn at the National Institutes of Health. "He went on and on as, I suppose now, guilty husbands do--'Isn't she wonderful? Isn't it fabulous all this work she is doing for them?' In retrospect, that is really sick."

"It's been very difficult," said another friend of Marianne's divorce ordeal, "but frankly, the meaner he is, the easier it gets."

On the other hand, both Gingriches were back in familiar patterns.

Newt Gingrich met Marianne Ginther in 1981 at a fund-raiser. She was 30. She had just broken up with a married man and father of three whom she had dated for some time. Gingrich was still married to Jackie, his high school biology teacher. He had married her at 19, partly to get away from his stepfather's domineering ways; she was seven years his senior. They had two daughters, now grown. Gingrich served divorce papers on her as she lay in bed recovering from surgery from ovarian cancer. Within months, he married Marianne.

His timing remains impeccable. In May, Gingrich called his mother-in-law to wish her a happy birthday, then asked to talk to Marianne, who was visiting. He told her he wanted out. He did not tell her that he had a patient mistress waiting in the wings.

Callista Bisek, too, was a girl from a rural town who met Gingrich at a fund-raiser. This one was for former Republican congressman Steve Gunderson, who had brought her to Washington as an intern from their small home town of Whitehall, Wis., where Callista was known as a student of voice, piano and the French horn. Back in Whitehall, talk about Callista and Newt died down a long time ago. "That's old news," said the editor of the local paper.

In early summer, Marianne's friends called to tell her that Gingrich and Bisek were going about hand in hand. The Star tabloid made a splash by stalking the couple outside Bisek's Arlington town house, then tailing them to a French restaurant in Great Falls for a confrontation. Other tabloids chimed in. But the really big guns came from Gingrich--through his attorney.

He charged that the affair began because he and Marianne had been separated for six years, starting in 1987. This shocked not only her and his parents but also all the opponents who saw Marianne Gingrich on the campaign trail. Then, he claimed that he got a girlfriend because his wife had a boyfriend--and filed court papers demanding she 'fess up. He contended she had hired a private investigator to follow him around and complained that she had transferred assets out of their joint accounts.

Marianne, between carrying on as the chairman of her local Red Cross office in Atlanta and dabbling in some consultant work, fired back with a set of interrogatories that included this request: "Identify the names and addresses of any and all persons, other than your wife, with whom you've had sexual relations during this marriage."

And this: "Do you believe that you have conducted your private life in this marriage in accordance with the concept of 'family values' you have espoused politically and professionally?"

Gingrich answered that question last week, said his attorney Evans, but he wouldn't say how.

CAPTION: Marianne Gingrich, above, Newt's wife for 18 years. Below, Callista Bisek, his girlfriend for six of them.

CAPTION:

CAPTION: Newt and Marianne Gingrich at a news conference in 1989.