Graves' disease, the thyroid malady diagnosed in President Bush, is one of the easiest of all the hormone disorders to cure, although patients often have to take medicine daily for a lifetime.

About 7 million Americans have thyroid problems of some description, and about 1 million of these are diagnosed as Graves' disease. About 50,000 new cases are discovered annually.In 1989, Barbara Bush was one of the new cases. On Tuesday, George Bush joined the number.

Since both Bush and his wife now have the disorder, theirs is a case of what doctors call "conjugal Graves' disease." It is considered rare but not unknown.

One of Bush's doctors, Dr. Kenneth Burman, a thyroid expert at Walter Reed Army Medical Center, called the White House phenomenon "just a coincidence" and said it does not suggest a contagion or an exposure to a common cause.

Medical science has yet to positively find the cause of Graves' disease. The disease is not thought to be caused by an infection or by some toxic in the environment. There is some evidence it may be triggered when the body's own immune system attacks the thyroid and causes it to secrete too much hormone.

Since thyroid hormone is sort of the metronome of the body - it helps to set the tempo for the heart, digestion and metabolism - too much can cause processes to speed up. The heart can race, blood pressure rise and the person can become agitated and have trouble slowing down for sleep.

Medical specialists said the president's treatment follows a classic pattern that leads to total and complete correction of Graves' disease in about 98 percent of the cases.

Dr. Burton Lee, the White House physician, said Bush's blood was tested for an excess thyroid after his heart problem surfaced. By Tuesday, three blood tests had shown the president had hyperthyroidism.

On Wednesday Bush was given a few ounces of a weak solution of radioactive iodine. Since the gland uses iodine to make its hormone, the thyroid ordinarily grabs and stores the needed chemical as it flows past in the bloodstream. The more active the gland, the more iodine it absorbs.

For Bush, the test results Thursday showed Graves' disease.

The doctors quickly ordered a new radioactive iodine cocktail for the president, this one 1,000 times stronger than the diagnostic dose.

Over the next few weeks, the radioactive iodine will disable the hormone-producing cells in his thyroid and the hormone levels will drop.

Burman said that since the irregular heartbeat was caused by excess thyroid, Bush's cardiac problem will be corrected as soon as the hormone levels return to normal. In effect, by destroying the thyroid, the heart condition is cured.

Doctors will monitor Bush's hormone levels for several months and Burman said the president eventually may develop a shortage of thyroid, a condition called hypothyroidism.

To correct this, the 66-year-old president will take a single pill of thyroid hormone daily for the rest of his life.

Burman said Bush should be "fully restored to a vigorous state of health very quickly."

Bush's hyperthyroidism was detected and treated very quickly, perhaps within six weeks of its onset. He suffered no major symptoms other than his irregular heartbeat.

Mrs. Bush was not so lucky. When her diagnosis was made two years ago, she already was suffering the bulging eyes and double vision common in Graves' disease.

In addition to taking her daily thyroid pill, she also must take drugs to control her eye problems. But Burman, who also treats Mrs. Bush, said "she has responded very well to treatment."