President Bush is taking rest periods in his private study to combat bouts of fatigue caused by his hyperthyroid condition, White House press secretary Marlin Fitzwater said.

"He's been tired," said Fitzwater on Wednesday. "The thyroid condition takes the energy out of him. He's been taking it easy. He relaxes and goes to his study in the afternoon where he sits in an easy chair for an hour or two."The normally active Bush has also curtailed his physical activity, on doctors' orders.

Bush is being treated for Graves' disease, the same ailment that afflicted his wife, Barbara, and Fitz-water said it will take a week or two for the president to adjust to the medication - digoxin, procain-amide, which doctors ordered to slow down his heart beat, and cou-madin, a blood thinner. He also has been taking an aspirin a day as a blood thinner.

Graves' disease was diagnosed as the root of Bush's rapid, irregular heartbeat, or atrial fibrillation, which he suffered May 4 while jogging at Camp David, prompting a weekend stay in the hospital.

Bush was given a dose of radioactive iodine, which will take a month or two to destroy his hyperactive thyroid. Fitzwater said Bush has not experienced a recurrence of atrial fibrillation.

Dr. Burton Lee, the White House physician, and his staff monitor the president's health several times a day. He described the president as "tired."

Bush appeared to have dozed during the entertainment in the East Room at the state dinner he hosted Tuesday evening in honor of Britain's Queen Elizabeth II.