ALEY, Lebanon - Nearly half the seats in Lebanon's parliament will be decided Sunday in the third round of a four-stage election held as Syria continues to cast a shadow over its tiny neighbor.

Polls opened at 7 a.m. in Mount Lebanon, the mountain region surrounding Beirut and stretching north and south of the city, and in the eastern Bekaa Valley near the border with Syria.

The vote in Mount Lebanon was considered a key to the election. It is the country's most populous region and a patchwork of religious sects and political factions that will decide Lebanon's direction after the departure of Syria's troops earlier this year.

Michel Aoun, a formerly staunch anti-Syrian army commander who has recently formed alliances with pro-Syrian factions, was among the first to vote Sunday. The Christian leader voted at a polling station in his hometown of Haret Hreik, where he was greeted by cheers and applause from about 200 supporters.

BEIRUT, - After two humdrum rounds of legislative elections, Lebanon is poised for a heated contest Sunday that could determine whether an anti-Syrian coalition will muster a parliamentary majority and maintain momentum to thrust the country into a new era.

In the most critical round of a four-phase election, Christian and Muslim voters in the central Mount Lebanon region and the eastern Bekaa Valley will decide on nearly half of the 128 seats in parliament.

At stake domestically is the new legislature's ability to dislodge remnants of Syrian control, after a 29-year military presence, from key institutions including the presidency. Syrian troops withdrew from Lebanon this spring, but the country continues to wield considerable influence.

"Syria is out of our geography, but not out of our politics or the region's geopolitics," Rafik Khoury, a columnist with the Al Anwar daily newspaper, said in an interview. "The difference is that a year ago, we were on death row. Now our sentence has been reduced to a one- or two-year prison term."

BEIRUT (Reuters) - Voters head to the polls in central and eastern Lebanon today (Sunday) , where anti-Syrian factions are squaring off against each other in the most crucial round of Lebanon's parliamentary election.

With 58 seats up for grabs in the Mount Lebanon and eastern Bekaa Valley districts, the shape of the next 128-seat assembly should become clear in the penultimate stage of Lebanon's first general election since Syria pulled its troops out.

Forty-two legislators have already been elected in the first two rounds of voting in Beirut and south.

Those rounds brought no surprises, with the son of slain former Prime Minister Rafik al-Hariri winning a landslide in the mainly Sunni capital and a joint Hizbollah and Amal slate sweeping polls in the southern Shi'ite heartland.

President George W. Bush issued a new warning to Syria to withdraw its forces from Lebanon, with the White House saying the Damascus government was having an intimidatory impact as Lebanon stages elections.

Bush said he was "disturbed" by reports that Syrian intelligence remain in Lebanon, in breach of a UN resolution ordering all Syrian forces out of the country.

"Our message to Syria -- and it's not just the message of the United States; the United Nations has said the same thing -- is that in order for Lebanon to be free," Syria needs to "not only remove their military, but to remove intelligence officers as well," Bush said at the White House.