ROME—Umberto Bossi, head of Italy's separatist Northern League, said he reached a preliminary agreement with Prime Minister Silvio Berlusconi about a key pension overhaul, as the country seeks to appease European pressure to accelerate the pace of its economic revamp.

Euro-zone heads of government have demanded that Mr. Berlusconi present by Wednesday a firm plan to boost Italy's stagnant growth and cut its huge debt. The prime minister held talks Tuesday with members of his ruling center-right coalition after a cabinet meeting...