Doctors believe that Senator Edward M. Kennedy of Massachusetts suffered a seizure at his home in Hyannis Port this morning, then a second seizure as he was being transported by helicopter from Cape Cod Hospital to Massachusetts General Hospital in Boston, according to an official briefed on the situation.

Kennedy's condition was unclear early this afternoon, as a special police security detail gathered at Mass. General. Kennedy family members were called this morning and told to rush to Boston, according to sources.

The Hyannis Fire Department responded to an emergency call requesting an ambulance at the storied Kennedy compound at about 8:19 this morning. The senator was rushed to Cape Cod Hospital. Shortly after 10 he was flown by helicopter to Boston, said Fire Lieutenant Bill Rex. The Cape Cod Times published a photograh of Kennedy, strapped to a gurney, being carried to the chopper.

Kennedy, 76, is the senior statesman in one of America's political dynasties. He was first elected in 1962.

In October, Kennedy had surgery to clear a blocked artery in his neck to prevent a stroke. At the time, MGH doctors said the one-hour surgery was successful and they expected Kennedy to make a full recovery. They did recommend he take aspirin to prevent blood clots after the surgery, in addition to medicine he was already taking to control high blood pressure and cholesterol.

Doctors described the extent of the buildup as "a very high-grade blockage" and said there was a slight chance it could recur in the next few years.

Kennedy's doctors said at the time the blockage, found in his left carotid artery, could have triggered a stroke by choking off blood flow and preventing oxygen from getting to the brain, or by breaking off and lodging in the brain.

About one-quarter of strokes are due to carotid artery disease. Carotid artery surgery is typically performed on patients who have had a stroke or an artery that is at least 70 percent blocked.

Kennedy felt no symptoms from the blockage, which was discovered from a routine MRI conducted to check on his spine, which was injured in a 1964 plane crash.

Patients with a neck artery blockage may have similar buildups of fat and cholesterol in other blood vessels, but Kennedy's doctors said there was no need for any treatment on his right carotid artery, and said he had passed a cardiac stress test prior to the surgery.

At the time, his personal physician deemed his overall health excellent and said he exercised daily and ate well. After a short period of rest, Kennedy returned to the Senate floor Oct. 30.

Before the surgery, Kennedy's only serious hospitalization is believed to have been after the crash of a small private plane more than 40 years ago. Kennedy suffered several fractured back bones, broken ribs, and internal bleeding in the crash, which killed two people.

Democratic presidential candidate Barack Obama, beginning a tour of hospitals in Eugene, Ore., told reporters that he had been in touch with the senator's family. "Ted Kennedy is a giant in American political history. He's done more for health care than just about anybody in history. We are going to be rooting for him. I insist on being optimistic about how it's going to turn out."

Kennedy gave Obama's presidential campaign a big boost this year with his endorsement and has campaigned actively for the Illinois senator.

Arizona Sen. John McCain, the likely GOP presidential nominee, said he awaited word on Kennedy's condition. "Senator Kennedy's role in the U.S. Senate cannot be overstated. He is a legendary lawmaker, and I have the highest respect for him. When we have worked together, he has been a skillful, fair and generous partner."