In places like the ballot box, the opinion polls, and the delegate count, George Bush's campaign for the presidency is in decidedly ill health. But there is one place -- P.O. Box 1980, Houston, Tex., the campaign's mailing address -- where the Bush campaign is doing quite well.

Every morning that the Post Office box is opened, it pours out more than 200 checks from people around the country who have decided that it is worth $200 or $500 or $1,000 to help Bush in his longshot effort to win the Republican presidential nomination over front-runner Ronald Reagan.

A similar scene is repeated every morning at the Kennedy-for-President headquarters on 22nd Street, NW. The daily mail bags produce a pile of checks that total, on an average day, well over $30,000.

It is an established axiom in the political industry that most contributors give their money as investments in a candidate they expect to win. The experience of the Bush and Kennedy campaigns supports that thesis only to a limited extent; both candidates are raising a little less money now than they did when they were still perceived to have good chances for victory.

The flow of money into the treasuries of these likely losers -- about $225,000 weekly to Kennedy and $150,000 to Bush -- suggests instead that there are thousands of people willing, even anxious, to make political contributions on the basis of principle.

"Yes, I did recognize at the time I contributed that he probably wasn't going to win," said H. Lawrence Fox, a lawyer from Alexandria who sent Bush $500 this spring. "I just thought he was a good man. There's nothing complicated about it. And I thought it was better to have two or more candidates for the nomination."

"I would send Kennedy more money today if they asked me," said Barbara Doyle, a high school teacher in Bristol, Conn., who contributed $20. "I don't suppose it would help now. I believe, I really do believe, that if the public, Joe Schmo, if they really knew where the two stood, they couldn't possibly go for Jimmy Carter. But I suppose it's over now."

A random survey of recent Kennedy and Bush contributors reveals that there are still some partisans who think the underdogs have a chance to win.

"I've never talked to reporters before, and I'll probably say something awful," said Rosemary Smith, a loyal Bush donor in Washington, "But I don't rule out a change at the convention. I think George could still come from behind on the balloting. I'll be up all night that night, watching for it."

The chance of victory is still the lure the candidates are using to attract contributions.

"We can win!" announces a Kennedy fund-raising appeal mailed to 35,000 Democrats this week. "I believe we can win all eight states on June 3 . . . I believe that in August at our national convention, the delegates will not vote to nominate . . . a sitting president . . . who, despite his political use of the powers of the presidency, is unable to win the key June 3 primaries."

"The race for the Republican nomination is turning into a tough, hard-fought battle," says the latest direct-mail burst from Bush, "and despite what the press says, we're going right down to the nomination. . . . We still have the second-highest number of delegates and it's delegates . . . that make the difference."

But that kind of analysis does not seem to be what spurs contributions at this stage. Even Rosemary Smith, the Bush fan, says it was admiration for the candidate, not any assessment of his chances, that moved her to give money.

"I knew his family, and they were wonderful people," Smith said. "Quote me on that.So I had a little party at my home, almost 60 people, not one of those you-pay-at-the-door things but one where they picked up an envelope on the way out and sent in what they wish."

Personal respect for the candidate and his accomplishments seems to be the most common spark of Bush contributions these days. Kennedy, too, has his share of donors who give out of admiration for the man, but the Kennedy contributors in general seem to have more ideological motivation.

"I hope he can win, I'd like to think he can, but I know he's behind, said Sid Stein, a Manhattan lawyer who paid $150 to attend a Kennedy fund-raiser. "But I bought my ticket because I believe in what he stands for and had stood for."

The point was made in narrative fashion by New York comedian Alan King, who presided at a $250-per-ticket Kennedy gala in Manhattan six weeks ago and told the guests about a doctor who had treated him during his boyhood in the Jewish areas of Brooklyn.

"My father sent the doctor $2 a week, regularly, every Friday," King said. "And he kept sending that $2 for years and years. I'm in college and my father's still paying the doctor. I'm in the Army -- still paying the doctor.Why? Because we owned. We owed for all the years he took care of us. And that's the way I feel about the senator in this campaign."

Another emotion that drives Kennedy backers to reach for their checkbooks is dislike of Carter. This is particularly true among ethnic groups.

"Kennedy has been with Greece on every vote," said Tom Sakellaridis, a restaurateur in New York City, who gave $500 after hearing Kennedy speak at a Greek-American club in March.