New Jersey Rep. Frank Pallone Jr. has called at least a dozen Democrats in the state to inform them he is running for Senate, according to a source who has spoken with the congressman.

Pallone was widely expected to run for Senate if a special election was held this year, because he won’t have to risk his seat to do so. The decision was essentially made on Tuesday, once GOP Gov. Chris Christie set the special election for Oct. 16, with the primaries scheduled for Aug. 13.

(See also in Roll Call: Christie Sets Special Election for October)

Newark Mayor Cory Booker is also likely to run for the seat, setting up what will be a competitive two-month sprint.

“For several months now, Mayor Booker has been taking the steps necessary to run, but he will make an official announcement at the appropriate time,” Booker spokesman Kevin Griffis said.

The candidates must move quickly, as petitions to get on the primary ballot are due in two weeks.

Christie will appoint someone to fill the seat of the late Sen. Frank R. Lautenberg, who died on Monday, for the next four months until the special election is held. He made it clear that person will likely be a Republican.

Republican sources said Christie’s short-list of potential appointees most likely includes former GOP Gov. Tom Kean, state Sen. Tom Kean Jr., state Sen. Joe Kyrillos and Lt. Gov. Kim Guadagno.