President Bush suffered shortness of breath while jogging at Camp David on Saturday afternoon and was evacuated to Bethesda Naval Hospital for treatment of an irregular heartbeat. A spokesman said the president was "relaxed, comfortable" and in good condition.

The 66-year-old president was diagnosed as having an atrial fibrillation, or irregular heartbeat. The condition can occur for a variety of reasons and does not necessarily represent a serious threat.Spokesman Marlin Fitzwater said the president was alert, stable and had no complaints. He said there was "no indication at this point that he had a heart attack."

He said the president's heartbeat was still irregular, however.

Fitzwater said there was no contemplation of transferring any power to Vice President Dan Quayle. "This was never considered to be that serious; there was never any question of the president losing consciousness and being unable to continue his functions," he said.

Bush had dinner with his wife, Barbara, at the hospital and was staying overnight.

Bush will be taking the medication Digoxin for several weeks, Fitzwater said. Digoxin, which is taken orally, is administered to increase the strength of the heartbeat while decreasing its rate.

Fitzwater said it was expected that Bush would leave the hospital on Sunday and that he hoped to return to Camp David.

Bush jogs several times a week, normally about two miles and frequently is accompanied by reporters and others. The president does not jog as frequently as he once did - five miles a day at his peak. He has slowed down in recent years on his doctor's advice.

Fitzwater said there were nowarnings before the episode, which manifested itself as unusual fatigue and shortness of breath. He said Bush "mentioned to his Secret Service agents that he thought he should check it out." Fitzwater said Bush then walked to the camp infirmary. Later, Fitzwater added, Bush walked to the helicopter and then into the hospital.

"He's in good spirits and ready to get back into the game," he said.

Vice President Quayle was at his residence in Washington, hosting a reception. His spokesman said the vice president was notified of the president's condition "a few minutes" after the episode occurred.

Quayle called Bush and spoke with him at 7:20 p.m. Fitzwater said White House Chief of Staff John Sununu had spoken with both Quayle and national security adviser Brent Scowcroft.

He said the doctors had indicated that Bush "could be back jogging in a matter of days," if he wishes.

Bush had gone to Camp David directly from Andrews Air Force Base earlier Saturday after returning from a one-day trip to Ann Arbor, Mich., where he spoke at the University of Michigan in the first in a series of planned college graduation speeches.

Bush, who turns 67 next month, had his last annual physical checkup March 27 and was proclaimed in excellent health by his personal White House physician, Dr. Burton Lee.

"The president continues in excellent health," Lee said at the time. "There were no surprises at the physical exam. He remains an extraordinarily vigorous man who continues to thrive on a great deal of physical activity and a rigorous, demanding work schedule."

Blankiston's New Gould Medical Dictionary defines atrial fibrillation as "a cardiac arrhythmia" - or an irregular heartbeat. Many people suffer from it at some point during their lives. The irregularity sometimes presents a fluttering feeling in the chest that goes away without the person being aware of anything more than a passing sensation.

A prominent sports doctor said jogging wouldn't cause an irregular heartbeat in someone with a history of running like Bush but that "vigorous exercise might bring out a cardiac abnormality."

"It can happen once and never happen again," said Dr. Lyle Micheli, director of sports medicine at Boston's Children's Hospital. "It can happen at that age just spontaneously. Whether it means there is an underlying problem, I really rather doubt it. Atrial fibrillation is really a benign condition."