Any race to succeed Kennedy would be crowded and fiercely fought.

Despite speculation that Kennedy’s wife, Vicki, could assume his Senate seat, family aides have said she is not interested in replacing her husband either temporarily or permanently. One of Kennedy’s nephews, former Rep. Joseph P. Kennedy II, has also been described as interested.

Other potential Democratic candidates include state Attorney General Martha Coakley, U.S. Reps. Stephen Lynch, Michael Capuano, Edward Markey, James McGovern and William Delahunt, and former Rep. Martin Meehan, now chancellor of the University of Massachusetts at Lowell.

On the Republican side, potential candidates include Cape Cod businessman Jeff Beatty, former Lt. Gov. Kerry Healey, former U.S. Attorney Michael Sullivan, state Sen. Scott Brown and Chris Egan, former U.S. ambassador to the Organization for Cooperation and Development.

The succession law was changed in 2004, when Sen. John Kerry, D-Mass., became his party’s presidential nominee and Republican Mitt Romney was the state’s governor. Before the change, the governor would have appointed a replacement to serve until the next general election.

That would have created the opportunity for Romney to install a fellow Republican in office, a move that Democrats who control the state legislature sought to prevent.

Last week, Kennedy asked Massachusetts lawmakers to change state law to give Patrick, a fellow supporter of President Barack Obama and a backer of Obama’s health care overhaul, the ability to appoint an interim replacement should he be unable to continue serving.

“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 said in a letter to Patrick.