[cnn-photo-caption image= http://i2.cdn.turner.com/cnn/2009/images/08/26/art.kennedysenate.0826.gi.jpg caption="It may be months before the Senate seat of Edward Kennedy is filled."]
(CNN) - It may be months before the Senate seat of Edward Kennedy is filled, following his death at the age of 77 on Tuesday.
A long-term vacancy could have effects far beyond Kennedy's home state of Massachusetts, since his death deprives the Democrats of the 60-vote "supermajority" with which they can theoretically force laws through the Senate despite Republican objections.
Under Massachusetts law, a special election must be held 145 to 160 days - about five months - after a Senate seat becomes vacant. The winner of that election serves the remainder of a senator's unexpired term.
Just last week, Kennedy urged that the law be changed to allow the governor to appoint a temporary replacement until the special election can be held.
In a letter to Gov. Deval Patrick and other state leaders, Kennedy said he supports the current law, but added, "I also believe it is vital for
(Massachusetts) 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 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."
The letter is dated July 2 but was not sent until August 19 - less than a week before Kennedy died.
Kennedy, who had been having conversations with several top state Democrats about a potential succession, was concerned that releasing the letter would disrupt intense and tumultuous Senate health-care negotiations, a source close to the senator said.
The only reason Kennedy sent the letter when he did was because the Boston Globe newspaper learned about the discussions and was prepared to print what he thought was an inaccurate account of his efforts, that source and another person close to Kennedy said. He therefore decided to make his desires clear by delivering the letter, knowing it would go public.
Kennedy has championed universal health care for years and wanted to make sure Democrats have the votes they may need for passage of a comprehensive bill.
He called the issue "the cause of his life," and hoped to see legislation that would "guarantee that every American will have decent, quality health care as a fundamental right," as he said at the 2008 Democratic Convention.
Democrats - who, in collaboration with Independent Sens. Joe Lieberman of Connecticut and Bernie Sanders of Vermont, now control 59 of the 99 occupied seats 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 was unable to attend many sessions for months due to his illness.
Until 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 - when Republican Mitt Romney was governor.
Critics charged the Democrats were trying to prevent Romney from replacing Kerry with a Republican in the event of a Kerry victory over
then-President George W. Bush.
It is not at all clear who will replace Edward "Ted" Kennedy in the seat he held since 1962. He died 15 months after being diagnosed with brain cancer.
His brother, the late President John F. Kennedy, had the seat for almost eight years before being elected to the White House in 1960.
The old law may have helped the seat stay in the family. When John Kennedy was elected president, Edward Kennedy was not yet old enough to be a senator. Kennedy family friend Benjamin Smith was appointed to the seat, but did not run in 1962 when John Kennedy's term expired - clearing the way for Edward Kennedy.
The seat may remain in Kennedy hands. Edward Kennedy's sons, Edward Kennedy Jr. and Rep. Patrick Kennedy of Rhode Island, have been tipped as possible successors, as has his nephew, former Rep. Joseph P. Kennedy II.
His wife, Victoria Reggie Kennedy, has no interest in filling the seat, one of the sources said.
Kennedy was last re-elected in November 2006. His term runs until January 2013.
- CNN's Dana Bash and Martina Stewart contributed to this report.