Kennedy, 77, who has brain cancer, sent a letter to Gov. Deval Patrick, State Senate President Therese Murray, and House Speaker Robert DeLeo, all Democrats, seeking action that would let Patrick appoint a temporary successor, should that become necessary, to serve until a special election is held.

Kennedy, first elected to the Senate in 1962, is chairman of its Health, Education, Labor and Pensions Committee. During treatment for his cancer, he has been absent for much of the wrangling about President Obama's push to revamp the U.S. health-care system.

Kennedy's letter said he supported current state law requiring a special election within 145 to 160 days after a Senate vacancy. That law was enacted in 2004, when Sen. John Kerry (D., Mass.) was running for president. It replaced a procedure that would have let the then-governor, Republican Mitt Romney, appoint a Republican successor.

With a Democratic governor, Kennedy's request would let Patrick keep Democrats from losing one vote on health legislation if he dies or cannot fulfill his duties.

"I strongly support that law and the principle that the people should elect their senator," Kennedy said in the letter, reported in the Boston Globe. "I also believe it is vital for this commonwealth to have two voices speaking for the needs of its citizens and two votes in the Senate."

Kennedy urged Patrick to appoint as an interim replacement only someone who has made "an explicit personal commitment not to become a candidate in the special election." The senator's wife, Victoria, has told friends she does not want the seat, the Globe reported.