WASHINGTON (CNN) -- Sen. Ted Kennedy, who is battling brain cancer, is urging Massachusetts officials to change a law to allow for an immediate temporary replacement should a vacancy occur for one of his state's two Senate seats.
Under a 2004 Massachusetts law, a special election must be held 145 to 160 days after a Senate seat becomes vacant. The winner of that election would serve the remainder of a senator's unexpired term.
Kennedy, a Democrat who has represented Massachusetts in the Senate for nearly 47 years, was last re-elected in November 2006. His six-year term ends in January 2013.
In a letter to Gov. Deval Patrick and other state leaders, Kennedy said he supports the current law, but adds, "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 during the approximately five months between a vacancy and an election."
Kennedy, 77, asked the governor and state leaders to "amend the law through the normal legislative process to provide for a temporary gubernatorial appointment until the special election occurs," according to the letter, dated July 2.
The letter was not sent until Wednesday, in part because Kennedy has been dealing with the recent illness and death of his sister, Eunice Kennedy Shriver, according to a source close to Kennedy.
Kennedy, who had been having conversations with several top state Democrats about a potential succession, also was concerned that releasing the letter would disrupt intense and tumultuous Senate health-care negotiations, another source close to the senator said.
"He's talking about his potential vacancy here, and the threat of Kennedy's vote on health care is a powerful incentive to get it done," the source said in reference to the senator's thinking over the past few weeks. "If the letter gets out, it could have a negative impact."
The only reason Kennedy sent the letter this week was because the Boston Globe learned about the discussions and was prepared to print what he thought was an inaccurate account of his efforts, both sources said. He therefore decided to make his desires clear by delivering the letter, knowing it would go public.
One of the sources described how "tough" the letter was for Kennedy to write, acknowledging it is likely he soon will no longer be in the Senate.
The senator's wife, Victoria Reggie Kennedy, has no interest in filling the seat, one of the sources said. Sen. Kennedy has held it since his first election in 1962. His brother, the late President John F. Kennedy, had the seat for almost eight years before being elected to the presidency in 1960.
Democrats, who -- in collaboration with Independent Sens. Joe Lieberman of Connecticut and Bernie Sanders of Vermont -- control 60 votes in the 100-member Senate, face a tough battle this fall on President Barack Obama's health-care reform package. They have been trying to calculate votes without Kennedy, who has been unable to attend many sessions for months due to his illness.
Kennedy has championed universal health care for years and wants to make sure Democrats have the votes they may need for passage of a comprehensive bill.
He has called the issue "the cause of his life," and hopes to see legislation that will "guarantee that every American will have decent, quality health care as a fundamental right," as he said at the 2008 Democratic Convention.
"It's typical of Ted Kennedy to be thinking ahead, and about the people of Massachusetts, when the rest of us are thinking about him," Patrick, a Democrat, said in a written statement.
Prior to 2004, Massachusetts law allowed the governor to appoint an immediate replacement in the event of a U.S. Senate vacancy. The heavily Democratic legislature changed the law, however, after Massachusetts Sen. John Kerry became the likely Democratic presidential nominee.
Critics charged the legislature with changing the statute to prevent then-Gov. Mitt Romney, a Republican, from picking a replacement for Kerry in the event of a Kerry victory over then-President George W. Bush.
"When this was an issue five years ago, Republicans pushed for an interim appointment but it was overwhelmingly rejected," Massachusetts House GOP Leader Bradley Jones said in a statement released Thursday.
"Out of political expediency and convenience, the Democrats are again considering showing a complete disregard of the democratic process and the laws of the Commonwealth by contemplating a change to the law to serve their partisan interests as opposed to simply what is the best and most appropriate policy."
Kennedy is currently the second-longest-serving member of the Senate, surpassed only by Democrat Robert Byrd of West Virginia. Calculations on Senate votes this fall also have included Byrd, who is 91.
-- CNN's Dana Bash and Martina Stewart contributed to this report.
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