The delay follows three days of talks by Amr Moussa, the secretary-general of the Arab League, with political leaders in Beirut, the capital, endorsing a so-called 'Arab plan', calling for the election of General Michel Suleiman, the army chief.
What is also demanded is the formation of a national unity government and the drafting a new law for parliamentary elections.
Hours before the official delay, a senior political source said the session was set for delay to allow more time for talks.
"There is a need for Moussa to continue his talks with various parties," said the source.
Moussa acknowledged differences remained and hinted of a delay, telling reporters in Beirut: "Lebanon's problem is heavy and needs more time."
Moussa has held talks with many leaders from both camps since arriving in Beirut on Wednesday.
He met Hassan Nasrallah, the Hezbollah chief, on Thursday.
Lebanon has been without a president since the term of Emile Lahoud ended on November 23.
Moussa failed in two previous attempts to broker an end to Lebanon's worst political crisis since the 1975-1990 civil war.