The area had hitherto been controlled mostly by Jumblatt's Progressive Socialist Party (PSP) and its fighters.
The violence came a day after Hezbollah accused Jumblatt's supporters of killing two of their members and kidnapping a third.
Machinegun fire and loud explosions rocked several Druze villages in the Chouf district, including Aaytat and Baysur.
As the fighting raged there, black smoke was seen billowing from several villages.
The violence later spread to the towns of Kayfoun, Qamatiye, Bchamoun and Shwayfat.
Plea to rival
Afterwards, Jumblatt, tacitly conceding the loss of his Chouf stronghold, urged Talal Arslan, a Druze rival allied with the Hezbollah-led opposition, to place the affected regions under army rule.
He said "things [had] deteriorated in the area of Aley in such a way that is threatening the coexistence with our Shia brothers".
"I agreed with [Nabih] Berri [the parliamentary speaker] to entrust Talal Arslan with seeking to put an end to all the fighting," Jumblatt said.
"I say to my supporters that civil peace, coexistence and ending the destruction [must] prevail over all the other considerations."
Jumblatt's statement came as the number of dead and wounded continued to rise.
"From the day the unrest started, 42 people have been killed and 164 wounded across the country," a Lebanese security official said.
In Beirut, Siniora, the Lebanese prime minister, and some of his ministers and staff observed a moment of silence at the government building in honour of those killed in violence.
Opposition fighters seized much of the city on Friday after battles with government supporters.
But Beirut is now coming under the control of the army after opposition forces were ordered to stand down by their commanders.
However, the opposition says it reserves the right to lead a campaign of civil disobedience until its political demands are met.
Al Jazeera's Rula Amin, reporting from Beirut, said Sunday's fighting can be considered "round two" of the conflict.
"This is a significant move. Walid Jumblatt was, through history, a prominent leader in the mountainous areas of Lebanon," Amin said.
"He fought in the civil war and his fighters have a reputation for their viciousness.
"Now he is asking the opposition to quell the violence, as they seem to be in control of the area."Tripoli battles
Earlier on Sunday the army moved into Tripoli, where fierce clashes left one woman dead and at least five people wounded overnight.
The fighting, which continued throughout the night, came hours after Lebanese opposition forces started to withdraw from the streets of Beirut.
An Al Jazeera correspondent reported on Sunday that all groups involved in the Tripoli clashes had agreed on a truce to allow the evacuation of injured people.
|For more on the situation in|
Lebanon watch Inside Story
An army officer said that pro-government fighters fought loyalists of an Alawite sect with links to Hezbollah in the Bab al Tebbaneh, Kobel and Jabal Mohsen neighbourhoods.
"One woman has died in her house near Bab al-Tebbaneh, and about 7,000 people had fled the fighting," the officer said.
Zeina Khodr, Al Jazeera's correspondent in Tripoli, said some members of the Alawite community told her that government supporters had started the fighting, although the claim could not be independently verified.
"According to the Alawites, the aim [of the government supporters] is clearly to show their power in Tripoli because they were clearly defeated in Beirut [by the opposition in recent days]."
Khodr said the army faced a challenge in remaining neutral for the benefit of all Lebanese people.
"The army is in a very difficult position - if it does attack one party the army may split along sectarian lines," she said.
Arab League decision
On the diplomatic front, Arab foreign ministers said after crisis talks in Cairo that they will send a high-level delegation to Beirut for dialogue with political leaders.
A resolution issued at the end of Sunday's meeting urged Lebanese politicians "to attend a meeting with a ministerial delegation ... in order to discuss the dangerous situation in Lebanon and draw up an urgent road map to implement the Arab initiative".
The initiative aims to bring together three opposition leaders (Nabih Berri, the parliament speaker; Michel Aoun, an opposition leader, and Hassan Nasrallah, the Hezbollah chief) and three government figures: Siniora; Saad Hariri, the parliamentary majority leader; and Amin Gemayel, a former president.
A delegation headed by Qatar and including Algeria, Djibouti, Jordan, Morocco, the United Arab Emirates, Yemen and Amr Moussa, the Arab League secretary-general, will head to Lebanon "very soon" for the talks, Moussa said.
The mission will intentionally not include Saudi Arabia and Egypt, which have been vocal in their backing of Siniora's government, as well as Syria, which backs Hezbollah.
The current fighting erupted after the government said last week that it would take action against Hezbollah's communications network