DOCTOR'S STATEMENT A statement issued Friday by Bill Bradley's campaign from one of his cardiologists, Robert H. Heissenbuttel: "Over the past month, Mr. Bradley has had reoccurrence of episodes of atrial fibrillation which have occurred without known trigger and spontaneously converted to regular rhythm within hours. These episodes have not in any way interfered with his busy schedule. "The natural history of paroxysmal atrial fibrillation includes sporadic increase in frequency of episodes, which does not indicate any change in heart status. Of importance, he only notes irregularity of the pulse and has no other symptoms. And the rhythm spontaneously reverts to regular. He has been advised to continue all normal activity without limitations."

CLINTON, Iowa -- Bill Bradley sought a final-weekend focus on tuning his political organization, but struggled to move the focus of his presidential campaign beyond discussions of his irregular heartbeat.

While Bradley sought to discount the condition as merely "a nuisance," he was dogged throughout the day by shouted questions from reporters and even polite inquiries from backers.

"It is not a factor in the campaign or in conduct in office," said an exasperated Bradley. "If I'm sick at my stomach, do I have to tell you I'm sick at my stomach?"

Bradley's rival for the Democratic nomination, Vice President Al Gore, eased up, though he had previously set aside Friday to tout his health care plan and was questioned as he toured a hospital.

"He's out there campaigning, that's the good news," said Gore. "It's a routine matter."

Already trailing in polls in Iowa, and with Gore looking better in New Hampshire, Bradley found the health issue and his handling of the disclosures consuming his campaign as it headed into the final weekend before Iowa's leadoff nominating caucuses.

The subject took center stage when Bradley confirmed he'd had four episodes of irregular heartbeats since disclosing last month he suffered from that condition.

Reporters demanded to know why Bradley hadn't disclosed the episodes when they happened, and even backers conceded they had worries. At a rally in Muscatine, Bonnie Weeks told Bradley she'd seen a deluge of reports on television and asked him to set the record straight.

"I was wondering about his health," she said. "Is he going to be fit if we elect him?"

Looking stern, Bradley said there was nothing to fear, which satisfied Ms. Weeks.

"It's a common condition," said Bradley. "It's a nuisance for me and it shouldn't be a concern for you."

By contrast, Gore spoke to his largest crowd yet Friday night, drawing 1,000 students to Iowa State University to warn against overconfidence.

"We can't take anything for granted" in the hours remaining before the caucuses, Gore said. "We need to make the best use of every single one of those minutes and hours to get a big turnout."

Bradley aides had planned a midday briefing, but the candidate appeared instead in an effort to quell the health issue. Instead, the noisy press conference found the former New Jersey senator and pro basketball player on the defensive.

"No, I'm not worried about it," said Bradley. "This is a common condition, millions of Americans have it." At rallies in vote-rich eastern Iowa, he urged backers to focus instead on getting their people to the caucuses.

"If you make a few more calls and get 10 more people out to your caucus, we can do better than most people expect," Bradley said.

"There are three days left and we have a lot of work to do," he said. "We have some unfinished business."

Bradley sought to quell the uproar over his health late in the day, releasing a statement from his cardiologist.

"These episodes have not, in any way, interfered with his busy schedule," said Dr. Robert H. Heissenbuttel. "He has been advised to continue all normal activities without limitations."

"There's really nothing to deal with," said spokesman Eric Hauser. "You can't control what the heart does, so the timing is irrelevant."

There's some mystery about what triggers the episodes, and Bradley offered a layman's theory that a change in soft drinks may have increased his caffeine intake. That has led him to drop the cream soda he has been drinking since December. But he said he has no plans to see a doctor for a checkup.

"If he has a problem and it's something that won't go away, I think maybe in the long run he ought to say, 'I've got other things to do. I don't need the stress of being president,"' Joyce Brown, a 59-year-old Democrat, said between sips of coffee at a Colfax diner.

While many argued the furor will have little lasting impact, Bradley aides were nervous because it was consuming the final days of the caucus campaign. Aides once worried about dealing with an Iowa loss feared the margin could grow.

While Gore leads in Iowa, Bradley is much more competitive in New Hampshire, and Bradley's camp worries about Gore getting momentum with a big Iowa victory.