It is late and Sen. John C. Culver (D-Iowa) is beat. This is the ninth event of the day and the 18th Iowa town Culver has been in during a week's trip home, and the election which justifies his exertion is still 19 months away.

At Bushnell's Turtle Cafe, a restored Victorian pub in this college town, the Johnson County Democratic Party is holding a fund-raiser. The gimmick of the evening is a bumper sticker for sale for a buck: "Don't Blame Me , I Voted for Clark, who was defeated for reelection in November by a conservative Republican.

This bumper sticker infuriates John Culver - lights the short fuse to a famous temper. But as he begins his remarls to the gathering he doesn't let this show.

"I hope to run a campaign that moves us away from the negativism and the cynicism of today," Culver says, speaking of the 1980 reelection race that already preoccupies him. "I will call upon the best instincts of the American people . . . I'm sure it hasn't gone out of style to help those who need help most - it better not have, or the light has gone out in America . . ."

As he continues, Culver starts to shout, just as he does when he gets worked up on the Senate floor. The atmosphere in the pub has been all wisecracking and banter, but it only takes Culver about three minutes to transform it. Suddenly everyone is paying close attention and keeping still.

Culver reminds the audience bluntly that college towns like this one cost Dick Clark his Senate seat. The turnout among 18-to-30-year-olds in Iowa last november was 13 percent, he shouts. "That's on your conscience, not mine," Culver bellows at the 100 or so people in the room. And Clark's loss, he adds, is a symptom of the malaise of American public life.

Government "is going to continue to reflect greed," Culver shouts. "It's going to continue to reflect injustice. It's going to continue to reflect ignorance . . . And it's going to be obsessed with selfish preoccupations" unless Democrats like those in the rom fight for the progressive tradition.

"I'm going to give it everything I've got," Culver goes on, now fairly shaking the heads on the glasses of beer on the bar with his rasping, exhausted voice. "But John Culver's not going to carry the whole load in this election . . . is the future of this country worth a few hours of your time?"

And now the heart of the matter: "I don't want any bumper stickers like this about me," he shouts, pointing contemptuiusly at a table where the Clark bumper stickers are spread out. "I don't want that at all. Spend the money now! Make the effort now!"

Then, in the best Shakespearian tradition, Culver turns off his emotion and pauses for a moment. In a much quieter voice he adds:

"As you can see, I'm relatively indifferent about next year's election." His big, round face breaks into a grin, and the audience welcomes the chance to join in a laugh.

"Boy!" a man in the audience says to his neighbour. "I thought it was going to be rather low-key, but it didn't turn out that way!"

A few minutes later - at 10:30 p.m. - Culver leaves the bar, adjust himself into the front seat of a staff aide's Buick and lights a big cigar for the two-hour drive to Des Moines, his ovenight stop. "When do I get to go to bed early?" he asks the aide driving.

"Not tomorrow, but the next night," she replies.

Culver is one of the Gang of 24, the unusually large number of Democratic senators whose terms expire in 1980. Last year he was toying with the idea of giving up the Senate, whch he finds an exhausting and frustrating job, but when his friend and former aide Clark wad defeated by Roger Jepsen in November, he decided he had to run again.

Culver is a prime target for a number of New Right organizations, and particularly for the "right to life" movement, which claims credit for Clark's defeat last year. Rep. Charles Grassley (R-Iowa), a conservative farmer-politician who holds H.R. Gross' old House seat, has all but declared his candidacy against Culver next year.

Culver has spent a lot of time in Iowa since Clark's defeat, partly trying torally the Democrats who were demoralized by Clark's unanticipated defeat, partly to demonstrate by his own combativeness that he plans to fight to keep his Senate seat, and partly to try to articulate a public position for p a progressive Democrat in an era that appears uncongenial to that breed.

During the Lincoln Day recess in February, Culver made headlines and provoked editorials all over the state by slashing away at a handful of Democratic state legislators in Iowa who had voted to call for a constitutional convention to pass a budget -balancing amendment. These legislators weren't good Democrats, Culver charged - good Democrats wouldn't change their principles just to bend to a prevailing political wind.

On last week's trip home Culver stayed away from the controversy, but began to look for new rhetorical formulations that might carry him through the reelection campaign. The challenge, Culver believes,is to avoid being tagged as a free-spending big-government liberal by the conservatives without abandoning his basic political philosophy, which has always been liberal.

His objective last week, he said, was so express his "understanding of the new mood," to identify with "the pain of inflation" and impatience with government in general, while insisting that government can still help make a better country.

"No American should be able to say he never had a chance," Culver said in one speech. "We haven't achieved that goal but we keep trying."

The objective, he said, is to get the country "into a problem-solving mood where we can be good again." He talked repeatedly about a cynical, pessimistic malaise in the nation's public life that he would like to dispel.

What does this mean on specific issues? Culver says he isn't yet sure. He promises it won't mean abandoning his basic outlook - "that's why you're in public life, to stick to your principles," he said. He pointed happily to aninterview given by his likely opponent, Grassley, who told a reporter here that Culver "is intellecturally honest" and "won't shift his liberal voting habits just to win an election."

But Culver speaks out in favor of balancing the budget without "triggering a dangerous recession." He is critical of badly run government programs and talks about the need for congressional oversight of the executive branch. He promises a major legislative initiative to overhaul federal regulatory agencies. He did not propose any new progressive programs in his speeches here.

Culver talked repeatedly in Iowa about his great-grandfather, whose letters from the Civil War fron have just been published by the University of Iowa Press. The elder Culver was a convinced patriot and Calvinist who left a 19-year-old bride to follow "my duty" to go into the war for the Union.

The published letters were all laddressed to "My dear wife," and signed "your affectionated husband," The elder Culver once wrote, "after my God and my country, I love my wife . . ."

That earlier Culver's dedication to duty and willingness to sacrifice, the senator said again and agian, was the sort of model modern America now craves. The tack evoked a warm response at stop after stop.

"There's aterrible necessity to reaffirm faith," Sen. Culver said at the end ofhis trip home. CAPTION: Picture, SEN. JOHN C. CULVER