Gary Hart carries his own bags now.

There is no Secret Service with him, and instead of 100 national reporters trailing in a chartered 747, there are sometimes one or two. But usually there are none. Instead of a dozen staff aides there is one.

"Oh, I don't mind," he says as he shleps his rumpled canvas bags from a string of commercial flights to various chartered planes through the Midwest. "I was never into the hoopla anyway."

The one-time presidential candidate who shook the foundation of the Democratic establishment last spring by unexpectedly coming within reach of his party's nomination is out there campaigning once again -- this time for the man he so badly wanted to defeat.

He insists his moments of regret or wishfulness are just "fleeting," as he travels from a lonely and rainy shopping mall in Evansville to a spirited campus rally in Columbus, enthusiastically promoting his now "good friend," Walter Mondale.

Yet, it is hard to know how he really feels. When his aide tells him in St. Louis that some of the political columnists have suggested he would have done better in the last debate than Mondale did, his eyes widen and he smiles.

"I wanted to be there," he says. "I was really looking forward to it."

This could be Gary Hart's finest hour. Whether he could have defeated Ronald Reagan will never be known. But as polls and analysts continue to suggest that "independent" Hart supporters are turning to Reagan, and as Mondale continues to trail, the Hart speculation of what might have been heightens.

"I'm for you in 1988!" fans call from their cars and from apartment house windows as he passes.

"We'll see about that," he answers politely.

He listens with interest as reporters in Chicago and supporters in Indianapolis tell him he would be faring better than Mondale, drawing bigger crowds and attracting the swing voters necessary for victory.

But he won't indulge in such talk.

"Well, we really won't know that until November 6," he says. "To speculate why something is happening that may not happen is unproductive for me.

"I really believed I was going to be president in 1984. I am not a visionary or messianic figure," he says, using the same words that were sometimes used by critics to describe him during the primaries. "I thought I was going to get the nomination. I had a lot of confidence. I thought that if the party, first, and then the country, was ready for new leadership, then I would be the president. It was not."

So he is out there, the primary candidate who just wouldn't quit -- even when it was apparent that Mondale had the delegate count on his side -- now traveling thousands of miles in nearly all of the states, assuming the role of party player that he once rejected.

"No matter what else is said about Gary during this period, he wants to make sure no one can say that he did not go out and actively support the ticket," says Dottie Lynch, Hart's pollster during the campaign.

Walter Mondale tells people Hart was the first person to show up in his San Francisco hotel suite to pledge support after he won the nomination, and Hart's effort is expected to be reciprocated by Mondale with help in retiring his campaign debt of nearly $4 million.

He says his travels (generally at the expense of the Mondale campaign) have nothing to do with a desire to run in 1988. But his old cadre of advisers differ. They say that in preparation he may not even run for reelection to the Senate in 1986.

Friends and the journalists who have covered him take note of a new, looser Gary Hart -- a dramatic departure, and what some see as a conscious one, from the man often described as cool and detached.

"That suggests one of two things: that I have changed or that they didn't have me right in the first place," he says. "I have always been a team player. The image was loner, cool, aloof -- all of which was wrong. You don't hear cool and aloof anymore and you don't hear loner. I was never any of the above."

For one, he looks a lot better than he did during those final primary days, when his already thin face had the added problem of being colorless and weary. ("It's amazing what sleep and square meals will do for you," he says.) His mood is as good as many people remember it, as he launches into his own singing rendition of "On the Road Again" while flying on the Mondale campaign plane, jokingly dances cheek to cheek with a stewardess, and even bursts out laughing when a reporter brings up a sore topic: his Teddy Kennedy imitation (for which he eventually apologized to Kennedy).

"Ho, Ho, Ho!" Hart laughs in a mock guffaw when he was jokingly asked to do it by a national political reporter at a Chicago fundraiser.

He is even making jokes about his age, which had turned into a damaging campaign issue after it was discovered that he misstated his birth year on his official biography.

"I hate to bring up a touchy subject, but are you 48 yet?" asked Curtis Wilkie of The Boston Globe en route to Youngstown, Ohio.

"No, and I don't think I'm 47 yet either," quipped Hart. "I know the month and the day, but I always forget the year."

And his public appearances, once intense, and sometimes awkward, are now fiery and crisp.

"I AM NOT HERE FOR WALTER MONDALE OR GERALDINE FERRARO!!!" he calls out to a mob of supporters at Ohio State University.

"I AM HERE FOR MYSELF. I AM HERE FOR MY 18-YEAR-OLD SON AND MY 20-YEAR-OLD DAUGHTER. I CARE ABOUT THIS COUNTRY. I DON'T WANT RONALD REAGAN IN THE WHITE HOUSE!!!"

Throughout the long and bitter primary season, Hart was consistently portrayed as the outsider. His surprise New Hampshire victory catapulted him and his campaign of "New Ideas" to the forefront, as Mondale demanded to know "Where's the beef?"

While there always seemed to be something the voters could not understand about him -- complicated further by his misstating his age and changing his name from Hartpence -- it was his seeming distance from backroom politics that made him at once an attractive candidate and an uncertain choice.

He ran on a campaign of the "future," while constantly suggesting Walter Mondale was the candidate of faded, outdated politics. These days he is gracious about his differences with Mondale, calling out on the stump that "my differences with Walter Mondale are minuscule compared with my differences with Ronald Reagan."

"Nonsense, absolutely nonsense," he says when he is reminded of just how bitter the primaries got. "People just didn't understand what was going on. It was never personal. We disagreed on trade policy. We disagreed on some things."

What about his comment that the nation was in "shame" under the Carter years?

"That was one phrase out of a 15-page speech on defense," he says. "I said, 'We don't want to go back to the days of shame of Iran.' It was one phrase in one speech. Is that vitriolic?"

But Hart has not totally forgotten the intensity of the primary struggle. "Mr. Mondale said some rough things about me, too," he says.

Said Mondale through a spokesman: "I don't think any public official has worked as hard in this campaign as Gary Hart, particularly generating deep enthusiasm, and strong support among young people."

"For someone who went through a battle with Mondale the way he did, and then get back on the trail -- I must say that takes a lot of guts," says Robert Beckel, Mondale campaign manager. "I must say I was somewhat worried at first."

Still, there have been some embarrassing moments. The Reagan campaign has targeted Ohio, a state Hart won, for ads that show clips of Hart criticizing Mondale and the Carter administration. A Mondale campaign worker in Columbus said that after the ads ran, several calls came into the Mondale office in Columbus from people complaining that Hart was a "traitor." Also, traveling throughout the state, Hart was forced to defend his feelings about Mondale because of the ads. ("Walter Mondale may pledge stable prices," one ad has Hart saying, "but Carter-Mondale could not cure 12 percent inflation.")

"Don't you have to swallow a lot?" demanded one Ohio reporter.

"I don't have to swallow anything!" he shot back.

It is hard to know when a politician's time has passed. George McGovern's had when he ran for the presidency a second time, and many feel it will be difficult for Teddy Kennedy to achieve the White House. But in Hart's case, so much of his campaign was unsophisticated in its operation, and unprepared for its successes, that only history will know if it was Hart the politician or Hart the technician who failed. "Who knows," he says kiddingly, "maybe Andy Warhol was right. I had my 15 minutes."

"I'm convinced more now than I was after the Democratic convention that Hart has a future," says Washington lawyer John McEvoy, who was a campaign adviser to Hart. "The message of 1980 was that the Democratic program is out of gas. If reaffirmed in '84, the Democrats ought to listen to people like Gary Hart who say that the party needs to come up with a program to incorporate social justice, but avoid the kind of something-for-everybody constituency approach that will have been repudiated twice if Mondale loses."

One thing is certain, though: Hart touched a core of voters, the independents, the young and first-time voters, and the so-called upwardly mobile Yuppies, who have been rejecting the old liberalism of the Democratic Party for Ronald Reagan.

"I am not a traditional politician, I am not a career politican," he says. "I haven't been around 20 or 25 years in politics and I think the call for new leadership and new directions was one that did strike a chord. And not everyone is able to make that call with the same kind of authority."

Despite his conscious effort to be looser, there remains some evidence of the old closed and controlled Hart during a ride to yet another midwestern airport -- this time en route from Detroit to Chicago.

He is asked if his post-campaign life has been an adjustment.

"To a degree, sure."

Could he talk about it?

"No."

Why?

He is laughing now, as he says: "I don't want to."

Could he try?

"It's boring. It's boring. Who cares about my adjustment? It's just obvious. People recognize you, they come up and say, 'I wish you were the candidate, I voted for you.' They're nice. Sometimes they ask for your autograph. They slap you on the back."

He says his family is a lot closer because of the campaign and that even his wife Lee is on the stump campaigning for Mondale.

When he is asked what he is trying to accomplish out there in the American heartland, what message he is sending on behalf of Walter Mondale, his intensity passes. He smiles mischievously and proclaims: "Come Home, Yuppie."