The agency, quoting White House spokesman Scott McClellan, reported that Bush had phoned Berlusconi to say he appreciated Italy's "strong stand" against terrorism following the March 11 train bombings in Madrid.
Bush also told Berlusconi Washington was grateful that Rome wanted its 1,500-strong contingent to remain in Iraq for a further period.
Berlusconi has been a strong Bush administration ally in the Iraq war despite strong public opposition to the conflict at home, heightened by the deaths of 18 Italians, including 11 paramilitary police, in a bomb attack last November.
Bush called Berlusconi a week after losing the backing of another staunch ally, Spanish prime minister Jose Maria Aznar, who last week was defeated in an election by the Socialists. Jose Luis Rodriguez Zapatero, the new Socialist prime minister, has said he will withdraw the Spanish contingent of 1,300 troops unless they become part of a U.N. peacekeeping force.