Fouad Siniora, Lebanon's prime minister, and Saad al-Hariri, leader of the majority in parliament, are among those from the government present at the talks.
Nabih Berri, parliament speaker, Mohammed Raad, a Hezbollah MP, and Michel Aoun, a Christian leader, are among the opposition delegates.
The latest developments coincide with a visit to the region by George Bush, the US president, who has accused Hezbollah and its Iranian and Syrian allies of setting out to destablise the country.
Plea for agreement
Both sides of Lebanon's political divide are discussing several issues at the meeting, which opened on Friday.
They are examining the make-up of a national unity government, especially the opposition's demand that all sides have the power to veto decisions.
Also, all sides must agree on a new election law before next year's parlimentary vote in June.
The presidency will go to General Michel Suleiman, Lebanon's army commander, if they resolve issues around the unity government and electoral law.
Finally, the leaders will discuss weapons held by Lebanese armed groups, which could prove to be the thorniest issue of all, given that Hezbollah has consistently refused to disarm.
The make-up of a national unity government, particularly a demand by the opposition that all sides have the power to veto decisions
The formation of a new electoral law
Lebanon's presidency will go to General Michel Suleiman, Lebanon's army commander, if the above issues are resolved
Weapons held by Lebanese armed groups, particularly Hezbollah, will be discussed
An Al Jazeera correspondent reported from Doha that both the government and opoosition have agreed to discuss a Qatari-drafted plan examining the future of Hezbollah's arms.
Rula Amin, another Al Jazeera correspondent in Doha, reported that there was a lot of hope that the talks would yield positive results.
"People have a lot of hope that it will work. However, they know that the issues are real. The political factions that are here have different interests, different concerns and have different visions for Lebanon," she said.
"It is not an easy job to bring them all together and to get them agree in a short time as well.
"Only a week ago, these leaders were talking to each other through the guns and there were bloody clashes between their supporters on the streets.
"However, there seems to be a will, not only among the Lebanese factions but also from the regional Arab countries and Iran, that this crisis has to be contained and an end to the violence has to be put."
Arab League plan
A six-point plan was approved on Thursday under the mediation of an Arab League delegation headed by Sheikh Hamad bin Jassim al-Thani, who is both Qatar's prime minister and foreign minister.
Under the deal, the rivals undertook to launch a dialogue "to shore up the authority of the Lebanese state throughout the country", to refrain from using weapons to further political aims, and to remove fighters from the streets.
It also called for the rivals to refrain from using language that could incite violence, as well as the removal of roadblocks that have prevented access to Beirut airport and other parts of the country.
Shortly after the six-point plan was announced, the opposition cleared a series of roadblocks leading to Beirut airport.
Air traffic came in to land at the airport shortly afterwards.
The Arab League intervention was prompted by the worst sectarian violence since the 1975-1990 civil war, marked by the takeover by opposition fighters from Hezbollah and its allies such as the Amal of large swaths of west Beirut.
Hopes of a settlement between the majority and the oppositon were raised on Wednesday after Siniora's government cancelled two measures against Hezbollah that were seen as the trigger for the latest unrest.
The cabinet rescinded plans to investigate a private Hezbollah phone network and reassign the head of airport security over allegations that he is close to Hezbollah.
Hassan Nasrallah, the Hezbollah chief, had branded those moves a declaration of war.
Parliament in Beirut is scheduled to convene on June 10 for its 20th attempt to elect a president.
Both sides agree on General Michel Suleiman, the army chief, as the new president, but they remain divided over the details of a proposed unity government and a new law for parliamentary elections due next year.
Six opposition ministers quit the Siniora cabinet in November 2006, sparking the current political crisis.