Philip Crane is talking, in his friendly, let-it-all-hang-out way, about what it's like to spend 567 days running for president, and the question arises: does he ever get just plain bored?

"Oh, yeah," Crane replies, as if this were the most obvious thing in the world. "You do get stale after a while. The other guys who are running tell me the same thing.

"Sometimes I get bored listening to myself talk -- like I'm going to fall asleep in the middle of the speech. That's why you take questions . . . but the questions get to be the same, too. You just start hoping somebody will ask something new, and then it's always the same."

Yet, despite the monotony of daily life on the have-speech-will-travel circuit and despite the minimal rewards of a campaign that has rung up a $600,000 debt with no significant gain in straw votes or opinion polls, Crane, the six-term Republican congressman from the Chicago suburbs, is pursuing the presidency today with the same chipper energy that marked his declaration of candidacy way back in August 1978.

Crane will tell you, in fact, that the odds against his winning are somewhat less astronomical now than when he started. This is so, he says, because the central anticipation of the Crane campaign may soon be realized.

"The premise on which I ran from the beginning," he explained with almost boyish eagerness in an interview a few days ago, "was that Ronald Reagan would eventually be reduced to mortal dimensions . . . and when he got in trouble, his support would turn out to be soft. Well, Reagan is really in serious trouble now . . . and we are in the best position to inherit the majority of his support."

To a degree, the Crane thesis comports with current fashions of thought among politicians, who say that if Reagan falters in New Hampshire on the heels of his second-place showing in Iowa last month, much of his following will go hunting a new leader.

But even if this happens, it is not so clear that the Reagan people will settle on Crane, who ran fifth out of seven in Iowa with 7 percent.

The standard shorthand picture of the entire presidential pack puts the contenders in a continuum ranging from Edmund G. Brown Jr. and Edward M. Kennedy on the left to Reagan and Crane on the right. Like most generalizations, this one ignores some particulars.

Reagan has moved to the center in recent years on such subjects as environmental protection and aid to the underprivileged. But Crane still boasts to audiences about his votes against major environmental bills and his reputation as the "biggest skinflint in Congress" on social programs.

Further, Crane's libertarian brand of conservatism doesn't fit neatly into the standard spectrum. He is so far to the right end of the continuum that he sometimes loops around and meets Brown and Kennedy at the left.

The basic impulse that "the government should leave people alone" is so strong in Crane that he has joined Brown and Kennedy in condemning President Carter's call for draft registration.

"Basically, I oppose a draft in peacetime," Crane said. "That's an intrusion on people's lives that you can't justify, because it is not the best way to field an army . . . and you can't escape the fact that any rational draft is by definition unfair. It doesn't make sense to draft Albert Einstein and put him in a foxhole just so you can say you ran a fair draft."

Similarly, Crane shares the Kennedy-Brown skepticism about Carter's declaration that the United States will defend Mideast oil supplies by force if necessary.

"When Carter says we're facing the gravest threat to peace since World War II -- that's baloney," Crane says.

"One thing the Russians know is you don't make empty threats. The Department of Defense says we couldn't defend the Middle East without using nuclear weapons. Does anybody realistically think we're going to launch tactical nuclear weapons over there?"

In one regard, candidate Crane in 1980 resembles candidate Carter of 1976; he is running as an outspoken Christian. This week Crane is broadcasting in New England one of the most unusual political advertisements of the current campaign -- a 30-minute sermon he gave to an evangelical gathering at a Bible college in Texas. In the ad, the candidate stands at a podium with a Bible open before him and explains that American democracy has succeeded because it is based on the Old and New Testaments.

Crane has budgeted $250,000 for New England advertising, a fact that angers former ally Richard Viguerie, the right-wing direct-mail wizard. Viguerie's firm is suing Crane for several hundred thousand dollars in back fees and Viguerie says Crane should pay the debt before he spends any more.

Crane, who is receiving funds these days from federal matching grants and from true-blue contributors, many of them solicited four or five times, says he can continue campaigning and still pay off all debts by the end of March.

One place Crane won't buy any advertisements is in New Hampshire's best-read paper, the Manchester Union Leader. A year ago the paper's vituperative editor, William Loeb, unleashed an extended "expose" that portrayed Crane, his wife and children as Bohemians with an excessive fondness for sex and drink.

These days, Loeb has moved on to a new target, George Bush. But the memory still hurts. "It was really a downer," Crane says. "It makes you wonder whether it is worth it, if this kind of thing is going to happen to your family. It just . . . it was very, very hard to live with."

One might also ask why Crane, a distinct underdog since Day One, has kept up the effort as long as he has. The answers are partly the same for Crane as for other politicians: Hope springs eternal, lighting may strike, etc., etc.

But the most important impetus of the Crane-for-president campaign has been the candidate's father, George Washington Crane, M.D., Ph.D., psychologist and conservative columnist, reared his five children to believe that public service is a duty.

"Dear Patriot," the elder Crane writes in a recent mailing to potential supporters, "Did you see the six Republican candidates in the Des Moines debate? Wouldn't you vote Phil Crane first in TV charisma?'"

The senior Crane, an earnest disciple of the as-the-twig-is-bent school of child rearing furnished the family dining room with a blackboard and used the supper hour for nightly lectures to his children on right-wing philosophy. Today when Philip Crane talks about his long uphill battle for the presidency, those lessons invariably come to mind:

"One of the things my dad taught us was that old saying, 'One man with courage makes a majority.' And when you think of that, it tells you you have no right to quit just because you're behind."