Stewart Mott, the Croesus with a cause, is furious. He's spent $85,000 and six months on John Anderson's campaign, and now the Anderson people have told him to keep his millionaire hands off. Anderson campaign strategist David Garth even snubbed him on the New York shuttle.

"I said, 'Hi, David,' " says Mott, who momentarily looks like a wounded animal, "and he glared at me."

Mott's is a classic case of campaign infighting spiced with celebrity and the gleam of inherited wealth. In February, he began raising money for Anderson. By May, there was his 65-point memo suggesting massive campaign reorganization. Anderson responded with a May 30 letter to the Federal Election Commission (FEC) calling Mott "disruptive" and his actions unauthorized. This week campaign officials released the letter, and the fracas went public.

Mott was out, they said. Too much meddling.

"Meddling?" says Mott, incredulously. "So help me, if your grandmother were to cross the street at Constitution Avenue during rush hour and I snatched her from the traffic, and then I saw you later that day and you said, 'You were meddling, I could think you were crazy.

"If there's a house on fire," he continues, although not quite as loudly, "and you have a bucket of water, then you do what you can to put it out."

Mott says he doesn't like headlines reading, "Anderson Boots N.Y. Billionaire," doesn't like to be given "the shaft," doesn't like any of these political conniption fits, but damn it all, he'll continue to work for Anderson. He's in his Washington apartment, just off the Wednesday morning New York shuttle, smoking a cigar, gray chest hair sprouting from his open-necked Levi shirt, more memos and press clips sprouting from tote bags.

For the last 15 years, this General Motors heir and liberal philanthropist has been (depending on your point of view) either putting out fires, saving grandmothers, or running Olympic-class political interference. He was the fifth son of a father who was worth $800 million, a son who was taught to ride a bike by a hired hand, sent to summer camp fat and lonely, and then graduated with honors from Columbia University. Eventually, he settled down to a career of giving away money.

It's a career and a fortune that have allowed him to carve a place for himself in liberal American politics, even though there are plenty who will say, as Garth did this week, that "if it weren't for his money he'd be answering the door." But the money did establish him as a well-known financial backer of the McGovern, McCarthy and Udall presidential campaigns.

"He wants to take charge of anything he's involved in," says Rep. Morris K. Udall (D-Ariz.), who explains that he took only $250 from Mott in 1976, "and many times he's in a position to do so. The events with Anderson are just part of a pattern in recent years."

"We've got to be in control," explains Michael MacLeod, Anderson's campaign manager, "and, ah . . . that doesn't allow for . . . ah . . . the way that Stewart operates, which is pretty much of a highly individualistic, uncoordinated way."

But Mott has his defenders. "He was a perfectly good participant in 1968," says former senator Eugene McCarthy, who accepted $100,000 from him that year. "He wasn't overbearing and meddlesome. We had problems with Garth."

And from an off-the-record veteran of the 1972 McGovern campaign, to which Mott contributed $400,000. "Look, I just don't want to do a number on him, because he does have a good side. And nobody will do a number on him on the record, either, because everybody's afraid they'll have to come back and ask him for help."

But in the Anderson campaign this week, Mott had become such an irritation that few, if any, seemed concerned about his loss. "There just came a point when all of Stewart's criticisms became so public, so widely distributed . . ." says MacLeod, trailing off.

Among the public criticisms was the 65-point campaign memo (sent to 300 people, according to Mott, and 1,500, according to Garth) which in section 1E referred to Garth as both "arrogant" and a "prima donna" who "quits twice a week."

"He's great, BUT," wrote Mott. "He turns off good people; doesn't listen well . . . will probably clash with you and Keke constantly. Try to keep him aboard, but don't rely solely on D.G."

Other bits of unsolicited advice from the memo, in which Mott constantly refers to Anderson as the presidential-sounding "JBA."

"Reach to Joe Citizen . . Good for the common touch to Mary & Joe Householder. Overcomes the aloof image.

"Plan your visits to England, France, Germany, Israel, Japan during the conventions -- you'll still surely get coverage. You need to meet Thatcher, Giscard et al., to establish your credentials in international relations, allay foreign press opinion that you're rooted in Rockford, best time is July & August, avoid Khomeini endorsement . . .

"I'll make you a bet. I'll put into a sealed envelope a prediction about where you'll be 45 days from now -- on ballot access, money, and polls. I bet that I'll be plus or minus 20 percent correct. I'll bet $100,000 personally. You can keep the envelope unopened for 45 days. Or open it now . . . Quit fudging!"

Says the veteran of the 1972 McGovern campaign who worked with Mott: "It's pretty hard to be on the fringes of any political campaign when the bands are roaring and the crowds yelling. That happens to anybody. There are always going to be people who think they should be somewhere other than where they are."

Mott, who at 42 says he gives most of his $2 million annual income to liberal politicians and causes like women's rights, population control and peace, hates to be branded the poor little rich boy.

"Look," he says, picking up the capaign memo from the desk in his Maryland Avenue office that doubles as bedroom, "it took a few brains to put this together. . .

"Some people think of me only as a millionaire, but there are a lot of dimensions to me and anybody who comes to that as a superficial judgment of me just hasn't done their homework."

Here are some other dimensions:

Gardener. He has a co-op penthouse on New York's Fifth Avenue with a rooftop full of 450 varieties of plants.

Husband. He wed Kappy Wells, a 31-year-old sculptor, last year and now brands married life "terrific."

Former, well-advertised bachelor."My social life," he wrote in a 1971 newsletter sent to 2,000 friends, "has been spent largely in the company of two young ladies -- separately, not simultaneously -- Kathy Aigner and Christine Donovan (alphabetical, not necessarily preferential order) . . .In addition, a delightful diversity of other young ladies had added spice and variety to my bachelor's life."

And, newsletter writer, like the one above. He sends them out every so often, complete with reply forms so that he can keep his mailing list up-to-date.

Speaking of newsletters, he's appalled by the one anderson sent out in June. He holds it up with two fingers, like a dirty diaper.

"This is one of those things like you're running for president of the sopho more class," he says. "Jesus. The libertarian Party has had a tabloid going for 12 months now. Full of news and substance. This is the best this campaign can do? It's s ---."

Still, he perseves.

"I don't like to be given the shaft," he says, "and I don't like to be treated shabbily. But wa nt to see Anderson elected president -- whatever the petty minds of some of his staffers."

But how's he going to do it? What now?

"I'm not quite sure," says Stewart Mott.