Syrian troops will withdraw to the Bekaa Valley in eastern Lebanon by the end of March, the two countries' presidents have agreed at a summit.
But they have not yet set a date for full withdrawal.
The announcement comes after weeks of international pressure and protests in the Lebanese capital Beirut.
France, Germany and the US have called for an immediate withdrawal of troops. The US wants all troops to leave Lebanon by May, in time for elections.
Up to 5,000 Syrian troops will leave outposts overlooking Beirut, but the fate of the 14,000-strong Syrian garrison has been deferred.
A joint Syrian-Lebanese statement said the "size and length of stay of Syrian forces in Bekaa" would be agreed a month after the initial redeployment.
The statement in full
After that, there would be further negotiations on a complete withdrawal.
The BBC's Kim Ghattas in Syria's capital, Damascus, says the statement was not specific on whether this meant a final pullout of all Syrian forces.
Syrian officials have worded their statements to leave room for their troops to remain just across the border in Lebanese territory, she says.
Some Syrian soldiers in Lebanon were seen packing, but no troop movements have been reported yet, our correspondent adds.
Tens of thousands of anti-Syrian protesters returned to Beirut's Martyrs Square to wave Lebanese flags and chant slogans calling for "freedom, sovereignty, independence".
It has been the scene of demonstrations ever since the death of former PM Rafik Hariri three weeks ago in a car bomb that many Lebanese blamed on Syria, although Damascus has denied responsibility.
There are also reports that unknown assailants have attacked Syrian workers sleeping in Mr Hariri's home city of Sidon, injuring three of them.
'Sacrifices' marked
Monday's meeting in Damascus between President Bashar al-Assad of Syria and Lebanon's Syrian-backed President Emile Lahoud appears to fall well short of international expectations for a Syrian pullout.
SYRIA IN LEBANON
Officials have been talking about a two-phase process in which troops would initially move to the Bekaa, and then deploy along the Syrian border.
At the meeting in Damascus, Lebanese presidential spokesman Rafik Shalala said Mr Lahoud thanked Syria for helping Lebanon after the 1975-90 civil war and "the sacrifices made by the Syrian army".
He said Mr Lahoud stressed continuing co-operation and "the unity of the Lebanese-Syrian position in confronting the challenges".
Peacekeepers
Syrian troops entered Lebanon in 1976 as peacekeepers during the 1975-1990 civil war, but have remained since, while Damascus has dominated Lebanese affairs.
The Syrian president said that after the redeployment, Lebanon and Syria "will have fulfilled our obligations under the Taif accord and under [UN Security Council] Resolution 1559".
The 1989 Taif accord, which ended the Lebanese civil war, stipulates a phased withdrawal, while the 2004 UN resolution calls for foreign forces to leave Lebanon and its militant groups to disarm.
The United States has kept up the pressure on Syria, saying Mr Assad's pledge was inadequate.
"It's clear to us, not just the United States, but the international community, that his words are insufficient," state department spokesman Adam Ereli told al-Hurra television.
"We have not heard the words: 'immediate and full withdrawal'," he told the US-financed Arab satellite channel.
Lebanon's pro-Syrian Hezbollah guerrilla movement has denounced what it sees as Western interference and called for a "massive popular gathering" in support of Syria on Tuesday.
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