Michael Kennedy, the 39-year-old son of the late Sen. Robert F. Kennedy, was killed this afternoon in a skiing accident at the posh Colorado ski resort of Aspen.

He was the second of Robert and Ethel Kennedy's 11 children to die tragically. His brother David died 13 years ago of a drug overdose, and other family members have been victims of what some have called a family curse.

Kennedy, whose alleged affair with a family babysitter tarnished the family political legend and may have prevented his brother from running for governor in 1998, died after colliding with a tree on an intermediate slope, according to a statement released by the Aspen Ski Co.

"Ethel Kennedy and her family are mourning the loss of their beloved son Michael, who was fatally injured while skiing with his family in Aspen," said a statement released by the resort, located in the central Colorado Rockies 162 miles west-southwest of Denver. "He was a special and wonderful father, son, brother, cousin and friend, and his family would appreciate your prayers during this tragic time."

Details of the accident that claimed Kennedy's life were sketchy tonight. Aspen authorities would only say that he struck a tree about 4:15 p.m. while skiing down the Copper Bowl ski run with several members of his family and was treated at the scene within four minutes by the resort's ski patrol.

"The ski patrol provided extensive first aid on the scene and transported Mr. Kennedy to an ambulance at the base of Aspen Mountain," the resort said in a prepared statement tonight. "On-mountain treatment included intensive cardiac care, spinal immobilization, and respiratory support."

Kennedy was transported to Aspen Valley Hospital 1 1/2 miles away, where he arrived at 4:51 p.m. and was pronounced dead an hour later, authorities said.

The run where Kennedy was skiing begins near the 11,212-foot summit of Aspen Mountain and is rated as an intermediate run. Weather conditions were clear and mild, and the resort said it had about a 25-inch base of packed powder snow at the time of the accident.

There were unconfirmed reports that Kennedy and the people he was skiing with were tossing a football back and forth as they descended the slope.

Kennedy's death "appears to be accidental," said the Pitkin County sheriff's office in a statement released tonight.

Rep. Joseph P. Kennedy II (D), whose plans to run for governor of Massachusetts were stymied by the publicity of his brother's alleged affair with the family babysitter, released a statement that read: "Michael's death is a terrible tragedy for his children, his wife, Vicki, and his entire family. We will miss him dearly."

Michael Kennedy, the sixth child born to the younger brother of the late President John F. Kennedy, headed a nonprofit organization that provides heating fuel to the poor. He also headed the reelection campaign effort of his uncle, Sen. Edward M. Kennedy (D-Mass.), in 1994, and was regarded as a likely candidate for Congress from Massachusetts.

In a statement, the senator said: "Vicki and I are heartbroken over Michael's tragic loss. Our thoughts and prayers are with Ethel, his children, Michael Jr., Kyle and Rory, and their mother, Vicki. We loved him and we will miss him very much."

But the sensational allegations of a long-standing affair with a babysitter -- beginning when the girl was 14 years old -- ended the political speculation about Michael Kennedy and provided grist for the Boston newspapers and national tabloids.

The Boston Globe, for example, reported that the alleged affair prompted marital problems between Michael and his wife Victoria Kennedy, the daughter of ABC sports commentator Frank Gifford. In 1995, sources told the Globe, Victoria discovered Michael and the girl in bed. The newspaper also reported that the long-running affair was one reason the couple announced in April that they had separated after 16 years of marriage. They had three children.

In July, Norfolk County (Mass.) District Attorney Jeffrey A. Locke announced that he had called off his investigation into charges that Kennedy had committed statutory rape, citing the babysitter's refusal to cooperate.

Responding in a statement, Michael Kennedy said: "I deeply apologize for the pain I have caused. I intend to do all I can to make up for the serious mistakes I have made, and to continue to obtain the help I need." He said earlier this year he was undergoing treatment for alcoholism.

His death on the ski slope unavoidably evoked a legacy of tragedy that has haunted the Kennedy family for decades, throughout its long and dramatic run on the American political stage.

For every Kennedy triumph, it seems, there has been an attendant death or disaster. First there was the death in 1944 of Joseph P. Kennedy Jr., the dashing oldest son of Joseph and Rose Kennedy, and thought to be the family's first political star. He was killed in a World War II aerial crash over the English Channel. Kathleen Kennedy, the oldest sister, died three years later, also in an air crash, followed two decades later by the assassinations of President Kennedy in 1963 and Robert F. Kennedy in 1968.

The younger generation has been unable to escape tragedy as well. Michael's brother, David, died of a drug overdose in Palm Beach, Fla., in 1984. Their cousin, Edward, the son of Edward M. Kennedy, lost a leg to cancer. Another cousin, William Kennedy Smith, was acquitted of a rape charge in Palm Beach in 1991, but the intense media coverage was withering and may have played a role in the babysitter's refusal to press charges against Smith's cousin Michael.

In a statement when the investigation ended, the family of the babysitter said that "a protracted investigation and trial, accompanied by unrelenting media coverage, would cause potentially irreparable harm to the victim of this outrageous conduct."

Michael LeMoyne Kennedy