MILAN — Silvio Berlusconi, former premier, announced a deal Monday with the Northern League — his fractious coalition partner in three governments — to jointly run in Italy’s election next month, a move that could give momentum to the center-right and extend the Berlusconi era.

While leaving open the question of whether he will run himself, Berlusconi underlined his ambitions for the deal reached overnight at his villa near Milan by saying: ‘‘Habemus Papum,’’ — the Latin phrase for ‘‘we have a pope.’’