HYANNIS PORT, Mass. | Smiling, waving, and flashing a thumbs-up, U.S. Senator Edward M. Kennedy walked out of Massachusetts General Hospital days earlier than scheduled, greeted well-wishers outside his family compound on Cape Cod, and immediately departed shore for a familiar refuge: the waters of Nantucket Sound.</p><p> For two hours, accompanied by his wife, Victoria, and beloved Portuguese water dogs, Sunny and Splash, Kennedy sailed his 50-foot sloop Mya in a light breeze. </p><p>The senator, wearing a red City Year jacket with “Ted” embroidered on the chest, stood at the helm, guiding the 1927 wood-hulled boat through the chop. He had talked about wanting to sail since being rushed to the hospital Saturday.</p><p> “It was wonderful to be on the water,” Kennedy said, shuffling off a dock after his return. “It’s all it takes.”</p><p> The very public show of vigor and resolve left little doubt that Kennedy, 76, intends to remain as active as possible while battling the malignant brain tumor with which he was diagnosed Tuesday.</p><p> Victoria Reggie Kennedy said her husband was driving her crazy and making her laugh with his insistence on racing this weekend in a Figawi regatta off Cape Cod. And officials at Wesleyan University said Kennedy was still scheduled to deliver the commencement address Sunday.</p><p> Friends said they were not surprised that Kennedy was active so soon after leaving the hospital, where he underwent a biopsy of his brain Monday. </p><p>They noted that he had faced tremendous adversity before — the assassinations of his brothers John and Robert and a plane crash in 1964 that badly injured his back. </p><p>Kennedy is also a fearless competitor in sports, said John P. Driscoll Jr., a friend of more than 50 years who has sailed with Kennedy, played tennis with him, and skied with him.</p><p> “He’s a hell of a competitor, and I know it will stand him in good stead,” said Driscoll, who first met Kennedy in the early 1950s, when he was a line coach on the Harvard football team and Kennedy was a hard-hitting end. “He’s a fighter and a warrior.”</p><p> Kennedy’s diagnosis of a malignant glioma, a cancerous tumor in the left part of his brain, raises the possibility that he will be unable to complete the final 4-1/2 years of his eighth full term. </p><p>Treatment typically consists of radiation and chemotherapy, but among the questions Kennedy is trying to answer this week are precisely what course of treatment to seek, where to seek treatment, and whether to try an experimental treatment.</p><p> “He will seek out the best and the brightest people who deal with this problem in oncology, and try to make the right decision,” Driscoll said. “I’m overall confident that he’ll not just make the right decision — he’s gritty enough to go through this. He’s overcome so many personal things in his life.”</p><p> U.S. Senator John F. Kerry spoke to Kennedy Wednesday just after Kennedy left the hospital, and said he sounded “upbeat, and positive, and just ready to go.”</p><p> “He was obviously thrilled to be out of the hospital and ready to fight,” Kerry said. “He’s in a fighting mood, and he wants to fight for the issues he cares about, and he’s obviously ready to fight for his health.”</p><p> Kennedy’s return to the public spotlight occurred after an extraordinary turn of events that started Saturday, when he suffered a seizure just before sitting down to breakfast at his Hyannis Port compound. </p><p>He was initially scheduled to remain at Mass. General through the end of the week, but was released early after his doctors said he had “recovered remarkably quickly” from his biopsy.