Moussa's visit came two weeks after a similar trip by David Welch, the US assistant secretary of state for Near Eastern Affairs.
Moussa described his talks with Berri as extremely important.
He said: "We have begun work which I think can serve as a basis for progress."
But Moussa's several visits to Lebanon in the past have yielded little results.
Lebanon has been without a president since Emile Lahoud, the pro-Syrian president's term ended on November 23 and parliament failed to elect a successor.
The divided parliament had agreed on Michel Suleiman, the country's army commander, as a consensus president but failed to elect him because the US-backed parliamentary majority and the Syrian-backed opposition led by Hezbollah cannot agree over power-sharing arrangements and the shape of the future cabinet.
The majority had rejected the opposition's demand for veto power over future government decisions.
A 19th attempt to elect a president has been scheduled for May 13. A previous session on April 22 was postponed amid continued disagreement.