When Robert C. (Bud) McFarlane quit his job last December as President Reagan's national security adviser, he said he wanted to spend more time with his family.

There were reports he wasn't getting along with the White House chief of staff, Donald T. Regan, and was weary of Cabinet infighting.

Only hinted at were rumors that McFarlane, a married man, was having affairs and that one reason he was getting out was that his personal life was a mess.

It was The Washington Rumor at its most vicious, and it had reached out and touched the 26-year marriage of Bud and Jonda McFarlane with its slimy finger.

The rumor surfaced last summer in Parade and rose again in two local magazines. Donald Regan himself -- and, more avidly, his assistants -- were also said to have passed the rumor along. However, when asked, the chief of staff denied having done this.

Now the McFarlanes sit on a cream-colored sofa in the immaculate living room of their ultramodern Bethesda home, sipping morning coffee.

"One of the really difficult things about something like this is that even your closest friends won't ask you about it, because nobody knows everybody really perfectly," says Jonda McFarlane in her bright, upbeat way. ". . . You can't go around wearing a sign that says 'It isn't true!' "

"In looking back, the strength of the marriage was, I suppose, what made [it] endurable," says her husband in his measured baritone.

It has been, he adds, a "surreal" time.

And, McFarlane now realizes, he may have "contributed inadvertently" to the rumors.

"Questions about why I left government never have really been answered," he says, "and I suppose I contributed to the murk by just simply saying that it was for personal reasons; [but] quite honestly, that was the only basis on which President Reagan said he would accept the resignation."

So McFarlane kept his mouth shut.

"[It] didn't seem to me in the national interest to go through all these who-struck-johns about the White House wiring diagrams and my relationship with . . . Cap and George and Don," he says.

Nor does he want to get into great detail now. But he's willing to say that Secretary of State George P. Shultz and Defense Secretary Caspar W. (Cap) Weinberger have views so "fundamentally different" that it led to "paralysis" in decision making. In addition, he says, there was "growing disorder" under Donald Regan's day-to-day management, so that policy advice went to the president "in a very chaotic fashion."

"I just reached the point where I didn't think that I could any longer accomplish what I wanted to in a policy sense," says McFarlane. ". . . And then, too, oh, uh, relationships in the White House just were no longer fun and professional."

There is, however, an up side to all this, says his wife.

"It's been very nice. He used to leave the house at 10 of 7. Now he leaves at 8 or 8:30. That's a big difference. That's another cup of coffee and a chance to visit in the morning."

A government limo used to come for McFarlane in the morning. Now he rides downtown to his new job at Georgetown University's Center for Strategic and International Studies aboard the Metro.

"It's a great system," he says of the Metro. "I like it."

McFarlane, 48, the son of William Doddridge McFarlane, a Democratic congressman from Texas, grew up in Washington, attending Woodrow Wilson High School here and then the U.S. Naval Academy. His wife, Jonda Riley, was born in Frederick and attended Bethesda-Chevy Chase High School, where she is now an English teacher.

They met in a Presbyterian church youth group, had their first date at his senior prom, and married in 1959, four days after he graduated Annapolis. They have a 24-year-old daughter who lives in Connecticut and 21-year-old twins, one of whom, a son, attends the Naval Academy.

McFarlane entered the Marine Corps and served 20 years before retiring as a lieutenant colonel. His was one of those military careers marked for stardom of one sort or another, and between combat tours in Vietnam he was sent to study strategy at the Institut des Hautes Etudes in Geneva.

While a Marine, McFarlane began working in the White House -- first in 1971 as counsel to President Nixon for legislative affairs; then as military assistant to Henry A. Kissinger in the Nixon White House; and later as an assistant to President Ford's national security adviser, retired general Brent Scowcroft.

McFarlane was deputy national security adviser when named by President Reagan to succeed William P. Clark in late 1983. He gained a reputation as a skilled insider -- poker faced, soft spoken, a man who shunned publicity and had access to the president.

Now he finds himself in an unaccustomed role, mounting a defense not against international enemies but against rumors of sexual misconduct.

References to the alleged affairs began last August in the personality column of Parade, a Sunday supplement distributed by The Washington Post and other newspapers. Names were not used.

"Just what's keeping the lid on the sex scandal involving a married top White House official and a White House reporter?" asked a supposed letter-writer. "And isn't the official also having another affair with a member of his staff?"

The magazine's answer: "The gossip has been hushed about in print and broadcast journalism circles. There is no conclusive evidence that it is true."

Parade Editor Walter Anderson now says, "I don't know that that was Bud McFarlane, or anyone else."

Local magazines picked up the item.

In October, Washington Dossier told readers to watch for reports of "a married White House official" having dual affairs. Then, in its January 1986 issue, The Washingtonian carried a juicy 500-word report, naming McFarlane, repeating the gossip and adding that chief of staff Regan was critical of McFarlane over the matter. Dossier followed with another item in February -- this time naming McFarlane.

Early this year, The Washington Post investigated the rumors about McFarlane and concluded that there was no factual basis for them.

How, then, did the gossip start?

"I think it probably started in the press corps," says McFarlane. ". . . The first I heard of it was in the wake of a summit in Bonn last spring. I had heard from a member of my staff who traveled on the press plane that someone had just started asking, 'Is there any private life to Bud McFarlane?' And as to the specifics that inspired that, I don't quite know."

One journalist who investigated the matter says the rumor may have started with an envious colleague of the female journalist who was getting some good scoops.

At first, the McFarlanes decided to say nothing and see if the rumors would die.

"Throughout this," he says, "Jonny and I talked to friends who said, 'Well, this is a kind of typical Washington story that you're foolish to take on, and the effect of that will be to sustain it,' and so we didn't, as maddening as it really was."

"The funny thing was," says Jonda, "I saw the thing in Parade and I thought, 'Who could that be?' We never had any idea that that, you know -- Bud didn't either . . . and we sat there and looked at each other and thought, and without any idea what they could be talking about."

Then, she says, friends in the press clued them in. "They knew that this was being said about us."

Finally, McFarlane says, he realized the problem wasn't going away and asked for advice from attorney Leonard Garment, whom he knew from the Nixon days. Garment advised a strong, public counterattack.

Says Garment: "He's one of the most decent people I know [and] I'm just interested in it being widely known that this story was a total fake right from the beginning. Stories like this mushroom and everybody accepts it as the truth. It's important in this city to counter that sort of thing before it gets too far."

After Garment approached Dossier, the magazine beat a fast retreat. A 190-word editor's note in the current issue concedes that the magazine failed to obtain comment from McFarlane before publishing the items, and adds that Dossier is "satisfied . . . that the stories and rumors concerning Mr. McFarlane's personal life are false."

John A. Limpert, editor of The Washingtonian, says discussions are under way with Garment as the magazine seeks to get from McFarlane the "full story of what happened to him as national security adviser. [Garment] didn't really ask for a retraction. He sort of got tough with Phil Merrill [the magazine's publisher] and Phil Merrill got tough back."

Jonda says Garment is helping the couple as a friend and refuses to take a fee.

"Len has been extremely professional and helpful," she says.

Last summer the McFarlanes purchased "this little log cabin that Jonny found in the Shenandoah" as a weekend retreat. The fast-paced White House life with its 80-hour weeks was cutting into their personal lives, says Jonda, and they needed "this very special place . . . It's wonderful. We could go and come in the same day; that was our goal, because in those days we thought we might have to do that."

The idea had come to them, she says, after "we spent a weekend with the Shultzes at their farm in Massachusetts and had a wonderful time, and it was a great introduction to us about what a weekend away could do for us . . . They're good friends, they're really very good friends. They were here last Friday night for dinner."

Not only were the families friendly, but McFarlane and Shultz saw eye to eye on the use of military force. McFarlane had taken his job one week before the Marine headquarters compound in Beirut was destroyed and both favored armed retaliation and keeping U.S. forces in Lebanon.

They were opposed by Weinberger and the Joint Chiefs of Staff. The debate continued, privately and publicly. McFarlane was overshadowed by the two powerful Cabinet officers, but he sought to resolve their differences, meeting with them for private weekly breakfasts.

Despite his exterior calm, the tension was eating away at McFarlane.

"You have two very, very fundamentally opposed individuals -- Cap and George -- both men of good will . . . each believing that they are expressing what the president wants. Now this cannot be. [It] leads basically to paralysis for as long as the decision-making model is a cabinet government where the president looks to his cabinet officers to be the center of policy initiative and advice."

Adds McFarlane: "That's very frustrating, to work in that kind of community."

McFarlane's problems increased dramatically, he says, after Regan took over as White House chief of staff Feb. 4, 1985, as part of the president's major second-term Cabinet shake-up.

In his slightly stilted, almost academic way, McFarlane says that Regan and his staff had begun to interfere in foreign policy matters in which they had no expertise.

"There occurred in 1986 a willingness on the part of other White House figures . . . to intrude into the policy process beyond their portfolios. It's entirely reasonable for the legislative shop to comment on the legislative effect of [foreign] policy, or the communications, or the political or the budget or whatever. But those things all go into the papers I write: 'This is the cost of Option X in each of those areas.' But when it became a matter of each of those opinions going laterally to the president in a very chaotic fashion, that's dysfunctional . . . There was growing disorder."

Regan, for his part, was said to resent McFarlane's private time with the president; and the idea was floated that McFarlane's briefings contained jargon and left the president confused.

Meanwhile, the rumors were circulating.

Finally, McFarlane says, he talked with the president privately and "at considerable length about the frustrations of trying to manage the national security policy community, ones of personality and of substance. And it became clear that while he understood those, he didn't want to make any changes.

"And I made it pretty clear that I just found it impossible to work under the circumstances that existed. But he said, 'Well, I'll never accept your resignation except for personal reasons.' And looking back, it was kind of foolish as I left to portray why I left as 'personal reasons.' "

McFarlane informed the president on the 1985 Thanksgiving holiday in California that he was leaving to spend more time with his family, according to a press report. On the plane returning to Washington, McFarlane talked with the president and Nancy Reagan.

Did they discuss the rumors?

"This issue never arose," says McFarlane, "and as far as I know, they still don't, may not be conscious of the whole flap."

The personal price has been high for the McFarlanes.

"Both of us have a very strong sense of public service as a high calling," says Jonda. "We felt very fortunate in the last five years that Bud was with the Reagan administration, because we have always been very lucky, people have always been very kind . . . and it wasn't until just recently that there has been a change in that situation."

Even so, she says, it's "the price you pay for being in public life."

"It was surprising," says her husband. "I guess, as Jonny said, it had never happened to us to have somebody say false things and be really mean about it."

Jonda: "I teach in a high school, and the kids read the newspapers, they see these things. I can't say anything to them, either. And they're less able to judge, maybe, than our mature friends are, about what's true and what isn't true.

"You feel that, really, the best defense over the long haul is to just be the people that you are; and over time it's apparent to people that things are okay, and that you're okay, and life goes on."

Their friends are supportive, if silent.

"People show support in various ways," says Jonda. "People who care for you, who don't want to ask, will invite you to their home more often, or do something nice for you, just kind of saying that, yes, they care. They're saying, really, 'We hope this isn't true. Even if it is true, we love you' . . . Nobody wants to talk about something like that."

Puts in her husband: "But some had the maturity of friendship to bring it up, and be very kind in asking, 'How can we help?' " Their pastor and a few friends from their church did this, he says.

On balance, the McFarlanes say, there are advantages to leaving public life for a time.

"You need to look in different directions," says Jonda, "take different views from time to time in order to be able to do what you do well. If you do it too long, you become less fresh."

"Jonny's right," says her husband. "I think it's probably healthy for the country for people that are in policy positions . . . to go out and absorb what other people are writing, and get some new ideas."

McFarlane has been active since his resignation. On Monday he appeared on "ABC News Nightline" to discuss the Libya raid. Yesterday he flew to Colorado to speak at the Air Force Academy.

"There's nothing quite as fulfilling to me as government," he says, "but I have to say that there are some interesting dimensions open in private life . . . I'm going around the country [giving speeches] explaining policy and listening to criticism I had never heard . . . and I enjoy that: meeting people in different sectors of private life -- business, academics, theologians, children, college kids."

At Georgetown's CSIS, McFarlane is supervising a study of Soviet-Third World relations.

He says he could even run for office.

"People have been kind in promoting the idea of elective office here in Maryland or in Texas or somewhere else. Maybe someday, although service in the executive branch enables you to have a much more direct effect on national policy."

He worries that he wouldn't be a good campaigner: "Occasionally I lose patience with people who don't know enough about issues and, gosh, that's wrong."

They sit on the couch together, smiling. He puts his arm around her for the photographer.

"It's good to have change in your life from time to time," she says. ". . . We don't have any regrets about that. Those were five very intense years" in the White House.

Her husband brightens: "And we expect to be back."