BOSTON — After the Boston Red Sox’s 86-year span without a World Series championship, perhaps the most familiar streak in Massachusetts is the half-century that a Kennedy has represented the state in the American Senate. Now, the news that Senator Kennedy has a cancerous brain tumor is forcing people to contemplate the day when he will no longer be there.

“It’s almost incalculable,” said Thaleia Schlesinger, whose brother, the former Senator, Paul Tsongas, toiled in Mr. Kennedy’s oversize shadow before resigning in 1984 to cope with cancer that eventually killed him in 1997. “He’s the go-to guy over and over again. You just look at the universities, the hospitals, the high-tech industry, education, never mind health care. He’s always been there.”

Immigrants lining up at the John F. Kennedy Federal Building, tourists strolling on the Rose F. Kennedy Greenway, and ordinary folks who received handwritten thank-you notes from the senator or a surprise distinguished visitor at a family wake pondered a future without Ted Kennedy.

“Forty-six years is a long time to be a senator. That’s got to count for something when it comes to delivering for the state,” said Ron Mills, who runs the shoeshine stand next to 122 Bowdoin St., the Beacon Hill address John F. Kennedy claimed when he served in the House and Senate and was elected president in 1960.

JFK served in the Senate between 1953 and 1960. Then Kennedy family friend Benjamin Smith warmed the Senate seat for two years until Ted Kennedy reached the minimum age of 30 specified in the Constitution. His Senate career is now the third-longest in the chamber’s history. Brian Hart of Bedford first met Mr. Kennedy in November 2003 at Arlington National Cemetery, when the senator attended the funeral of Mr. Hart’s son John, a soldier killed in Iraq. He recalled yesterday how the senator listened to

his story about soldiers and their vehicles lacking proper armor. Mr. Kennedy followed up by calling a hearing later that month.

Today every military vehicle in Iraq is armored. And within six months of Mr. Kennedy’s hearing, all American soldiers had been issued ballistic plates for their body armor.

“He’s a wonderful guy. Literally hundreds of people are alive because of his work and literally hundreds were not wounded because of his work,” Mr. Hart said. The 76-year-old Mr. Kennedy was diagnosed with a malignant glioma, an especially lethal type of brain tumor. Most such patients die within three years, sooner if they are older.

Yesterday, Mr. Kennedy was released from Massachusetts General Hospital in Boston and returned to the family compound at Hyannis Port to await test results that will help determine his treatment, which is expected to include chemotherapy and radiation.

Mr. Kennedy gave a thumbs-up to well-wishers and kisses to relatives as he walked out of the hospital. A square bandage on the back of his head marked the spot where doctors performed a biopsy on the brain tumor.

Mr. Kennedy’s dogs, Sunny and Splash, met him at the hospital door. Hospital employees and others applauded the senator.

Before he and his wife, Vicki, got into a dark Chevrolet Suburban, Mr. Kennedy kissed his daughter, Kara, and his niece Caroline Kennedy, and embraced his son Patrick, a congressman from Rhode Island.

On the road to the Kennedy compound on Cape Cod, neighbors placed signs welcoming the senator home. “We wish you well Ted, The Sullivan Family,” one read.

The Boston Herald, the conservative tabloid that has delighted for decades in ridiculing the senator, declared, “We’re with you, Ted” across its front page.

Mr. Kennedy took a walk on the beach with his dogs as soon as he got home.

“Good to be back home,” he told reporters before he and his wife headed off for a sail on his sloop, Mya.