WASHINGTON — People in Massachusetts suddenly are thinking the unthinkable: Who possibly could succeed Sen. Edward Kennedy, patriarch of the famed political family that has dominated the state for more than four decades?

The news about Kennedy's cancerous brain tumor has led to quiet speculation about whether he may try to handpick a successor, possibly paving the way for a relative to take over his seat.

The prospect of Kennedy's eventual departure also has touched off a scramble involving Massachusetts congressmen and others.

Kennedy, 76, is not up for re-election until 2012. But his medical condition has people wondering if he might resign before then or decline to run for another term. Given Kennedy's stature in the Democratic-dominated state, it's a sensitive topic that few in politics are willing to talk about publicly.

"There will be great respect and delicacy, of course," said Tufts University political science professor Jeffrey Berry.

Over the years, the Kennedys have not shied away from grooming family members for office.

In 1962, Kennedy won the Senate seat that his brother, John, held before winning the presidency in 1960.

The Kennedys helped arrange the appointment of John's old roommate, Benjamin A. Smith, to the seat until Edward Kennedy turned 30 and was legally old enough to run for the Senate. Kennedy has held the seat ever since.

With the senator's health now in question, Kennedy's nephew, former Rep. Joseph Kennedy II, D-Mass., is seen as a possible heir. He is sitting on about $2 million in leftover campaign funds.

But the younger Kennedy, who provides low-cost heating oil to the poor through Boston-based Citizens Energy Corp., has balked at running for governor in recent years and shows scant interest in jumping back into politics.

There is the possibility one of the senator's sons, Rep. Patrick Kennedy, D-R.I., or Edward Kennedy Jr., could seek their father's seat. Kennedy's wife, Vicki, has been mentioned, too. There are other Kennedys, too, who could decide to run.

Brown University political science professor Wendy Schiller, who studies Congress, doubts that a family member will succeed the senator, given the faded Kennedy mystique.

"The days when you could do that easily without any backlash — those days are gone," she said.

When the Kennedys maneuvered to win Edward Kennedy his Senate seat four decades ago, the family was intent on building a political dynasty and the Senate was seen as a launching pad for the White House, Schiller said.

"I don't see that necessarily happening with any of the second-generation Kennedys now," she said. "Kennedys can be effective in all sorts of arenas. They don't necessarily have to go to the Senate now."

Beyond the Kennedy clan, Massachusetts boasts a lengthy list of potential candidates from both parties:

• Possible Democrats include Gov. Deval Patrick; Martha Coakley, the state's attorney general; Rep. Edward J. Markey; Rep. Barney Frank; Rep. Stephen Lynch; Rep. Michael Capuano; and Rep. James McGovern. Former Rep. Martin Meehan, who resigned his seat to become chancellor of the University of Massachusetts-Lowell last year, has $4.8 million in leftover campaign funds.

• Potential GOP candidates include former Massachusetts Govs. Mitt Romney and William Weld.

Unlike most states, Kennedy's successor would be chosen by a special election, not the governor.

State law requires a special election for the seat no sooner than 145 days and no later than 160 days after a vacancy occurs. The law bans an interim appointee.

The law was changed in 2004, when Massachusetts Sen. John Kerry became the Democratic presidential nominee and Romney was governor. Before the change, the governor would have appointed a replacement to serve until the next general election.

That would have created the opportunity to install a fellow Republican in office, a move Democrats who control the state Legislature wanted to block.