One of Kennedy's nephews, former Rep. Joseph P. Kennedy II, has also been described as interested, although his office points out Kennedy has made no public statements on the matter.
Payne expects Michael Dukakis – who is "still much beloved in Massachusetts" – and Peter Meade – one of the state's "super citizens" – will be among those considered to temporarily fill Kennedy's vacant seat.
Several state politicians interested in running for the seat would likely prefer Gov. Patrick not make an appointment. Among the figures with expressed interest in Kennedy's seat is Martha Coakley, the first female attorney general in Massachusetts.
Other Democrats who might try to succeed Kennedy include Reps. Stephen Lynch, Michael Capuano, Edward Markey, James McGovern and William Delahunt.
Former Rep. Martin Meehan, now chancellor of the University of Massachusetts at Lowell, has $4.8 million in his federal campaign account, the largest sum of any potential candidate. That would give him the advantage in any special election sprint.
On the Republican side, potential candidates include Cape Cod businessman Jeff Beatty, former Lt. Gov. Kerry Healey, former U.S. Attorney Michael Sullivan and Chris Egan, former U.S. ambassador to the Organization for Cooperation and Development.
The 77-year-old Kennedy has been battling brain cancer since last spring, spending time with his family at their homes in Washington and in Hyannis Port, as well as a rental property in Florida.
He hasn't appeared on Capitol Hill for Senate business since April, and he was unable to attend the funeral for his sister, Eunice Kennedy Shriver, earlier this month.
Today, White House Press Secretary Robert Gibbs said the last time that President Obama spoke with Kennedy was a few week ago about health care. He said they did not discuss Kennedy's letter to state leaders.
"[Kennedy] has been fully engaged," Sen. Kerry told the Globe. "If [Senate Majority Leader] Harry Reid required 60 votes tomorrow, Ted Kennedy would be on a plane and be down in the Senate to vote."
ABC News' Rick Klein, John Berman, and Barbara Garcia and the Associated Press contributed to this report.