Prime Minister-designate Fouad Siniora presented a new 30-member government to President Emile Lahoud on Tuesday, and said Lahoud would give him a reply on Wednesday.
But strong reservations by Christian leader Michel Aoun and the Shia Muslim coalition over their representation in the cabinet made swift approval unlikely, the sources said. Siniora and Lahoud were expected to meet again on Thursday.
The bickering came the day after a pro-Syrian minister escaped an assassination attempt, raising fresh fears of Lebanon sliding into instability.
Siniora was insisting on his line-up and appeared unwilling to introduce changes, raising the possibility that he might opt to step down, they said.
The government is expected to be dominated by anti-Syrian politicians, most of whom turned against Syria after the assassination of former Prime Minister Rafik al-Hariri on 14 February, which pressured Syrian forces to quit Lebanon.
Siniora, who is loyal to Saad al-Hariri, leader of the largest bloc in parliament and the slain ex-premier's son, was asked two weeks ago to form the government.
Siniora drew up a cabinet of 24 ministers he had agreed with the Shia Amal and Hizb Allah groups and was close to winning the approval of Aoun, who leads a 21-member bloc in the 128-seat parliament.
"This has cast a climate of mistrust over the government issue. Therefore, the bloc links its participation in the cabinet with carrying out what had been agreed"
Statement by coalition - comprising of Christian leader Michel Aoun with Shia organisations Hizb Allah and Amal
But hours after Defence Minister Elias al-Murr was wounded in a car bomb attack near Beirut on Tuesday, Siniora presented Lahoud with the list adding six ministers, four of whom are loyal to Hariri, taking other groups by surprise.
Aoun's bloc said in a statement that it was suspending its participation in the government as Siniora had renegaded on an earlier agreement.
"This has cast a climate of mistrust over the government issue. Therefore, the bloc links its participation in the cabinet with carrying out what had been agreed," it said.
Amal and Hizb Allah also indicated they would not agree to the proposed line-up, which gives them five ministers.
Lahoud has repeatedly said he wanted government to reflect the size of each group's representation in parliament and he was likely to demand changes, the sources said.
Siniora, finance minister for most of the period after the 1975-1990 civil war and a senior aide to Hariri, faces the task of controlling a $36 billion public debt that has almost reached twice the size of Lebanon's gross domestic product.
He also needs to prove to international markets that Lebanon can take care of its internal security without Syrian troops and maintain unity as tension rises between pro-Syrian and anti-Syrian factions, the most powerful of which is Hizb Allah.