"An agreement has been reached," between the Western-backed pro-government majority and the Hezbollah-led opposition, MP Ali Hasan Khalil told reporters.

"We expect a (parliamentary) vote to elect a president on Thursday or Friday," he said, as the Doha talks moved towards a Wednesday deadline.

The details of the agreement were not revealed, but another opposition delegate who requested not to be named had said earlier that a joint committee formed to iron out differences over a decisive electoral law for parliamentary polls due next year had been "making final touches to a deal."

Lebanese rivals agreed last year on electing army chief General Michel Sleiman as a successor to Damascus protege Emile Lahoud, who stepped down at the end of his term in November.

But they have differed over shares in a proposed unity government and the electoral law.

The Syria- and Iran-backed opposition refused to put off discussion of the disputed electoral law, and insisted on getting a "blocking minority" in a proposed unity government.

According to the government delegate, a second proposal suggested a return to an electoral law adopted in 1960, which is no longer in force. That would require amendments to disputed constituency boundaries in the capital Beirut -- the bedrock of support for Sunni parliamentary majority leader Saad Hariri.

The current law gives Hariri virtual control over the 19 Beirut seats.

The second proposal would allow the opposition to compete on at least five of them.

Rival parties aim to secure as many as possible of the capital's 19 seats in the 128-member parliament.

Both proposals also offered the opposition the long-demanded blocking minority, the same delegate said.

Delegates from the U.S.-backed ruling coalition and the Hezbollah-led opposition told Reuters disputes over a parliamentary election law and a new cabinet had been settled on the sixth day of Arab-mediated talks in Qatar.

"The deal is done. The text has been written," an opposition delegate told Reuters. The official announcement was expected at 10.00 a.m. (3 a.m. EDT), he added.

A ruling coalition delegate also confirmed the deal, which will meet the opposition's long-standing demand for veto power in cabinet.

Hezbollah, a group backed by Iran and Syria, increased pressure on the ruling alliance this month by routing its followers in a military campaign. The Qatari-led negotiations built on mediation that ended violence which killed 81.

It was Lebanon's worst civil conflict since the 1975-1990 war and exacerbated tensions between Shi'ites loyal to Hezbollah and Druze and Sunni followers of the ruling coalition.

Qatari Emir Sheikh Hamad bin Khalifa al-Thani joined the Doha talks shortly before midnight after returning from Saudi Arabia -- one of the main foreign backers of the ruling coalition.

A deal paves the way for parliament to elect army chief General Michel Suleiman as president, a post that has been vacant since November because of the political deadlock. The vote in parliament could take place as soon as Thursday, delegates said.

The anti-Damascus ruling coalition had long refused to meet the opposition's demand for cabinet veto power, saying the opposition was trying to restore Syrian control of Lebanon.

Syria, a close ally of Iran, was forced to withdraw troops from Lebanon in 2005 following the assassination of former Prime Minister Rafik al-Hariri.

The United States has held up the withdrawal as a foreign policy success story.

But Hezbollah's military campaign this month was a major blow to U.S. policy in Lebanon and forced Prime Minister Fouad Siniora's government to rescind two measures targeting the Iranian-backed group.

The deal will include a pledge by both sides not to use violence in political disputes, echoing a paragraph in the agreement that ended the fighting. -With Agencies