Syria's stated intention to begin disengaging its military forces from this Mediterranean country poses the most serious challenge to the militant Shiite Hizbullah organization since the end of the 1975-1990 civil war.
A Syrian withdrawal threatens to deprive Hizbullah of its Damascus-sanctioned political cover to pursue an aggressive anti-Israel agenda. "What is at stake is Hizbullah's future as a militia, as an armed force, and also as a pan-Islamic movement," says Samir Kassir, columnist for Lebanon's leading An Nahar newspaper.
The choices facing the powerful organization are stark. If it chooses to adapt to the new realities in Lebanon, it is likely to face the isolation and eventual dismantling of its military wing, the Islamic Resistance, which drove Israeli occupation forces from south Lebanon in May 2000 and is now deployed along Israel's northern border. The Islamic Resistance has about 300-400 full-time guerrilla fighters and several thousand reservists.
Although Hizbullah has an extensive social-welfare network and an important presence in the Lebanese parliament, the Islamic Resistance is its beating heart. Dissolution risks turning Hizbullah into just another - albeit respected - party jostling for influence in a fractious political arena.
But if Hizbullah continues to defend Syrian interests in Lebanon and insists on retaining the Islamic Resistance, it could find itself on a collision course with a future Lebanese government, and risk alienating its vital support among the Shiite community.
"Hizbullah is at a crossroads," says a European diplomat here. "The leadership is taking it day by day, but I hope Hizbullah chooses the democratic option. There is no need to bear arms anymore."
Hizbullah has been under scrutiny since the Feb. 14 assassination of Rafik Hariri, a former Lebanese prime minister, which sparked unprecedented public demonstrations in Beirut calling on Syria to withdraw from Lebanon.
In a keynote address Sunday, Sayyed Hassan Nasrallah, Hizbullah's secretary-general, insisted that the Islamic Resistance is still required to defend Lebanon from potential Israeli aggression. "The resistance will not give up its arms ... because Lebanon needs the resistance to defend it," he told reporters after a meeting of loyalist parties.
On Saturday, following weeks of mounting pressure from Western as well as Arab nations, Syrian President Bashar Assad announced that Syria would move its 14,000 troops in Lebanon to the border, leaving it open as to when Syrian soldiers would completely withdraw. The defense minister said Sunday that a pullback would begin Monday.
Hizbullah has adopted a cautious policy of continuing to profess support for Syrian involvement in Lebanon while not criticizing the Lebanese opposition, calling instead for dialogue.
Sayyed Nasrallah continued that theme, saying "we are committed to peace and unity ... any breaches of security are forbidden ... if we have any differences we will resolve them in a civilized and democratic way."
Of all Syria's allies, Hizbullah is the only group with which the Lebanese opposition says it is willing to negotiate - a mark of the general respect many Lebanese have for the group, but also recognition of Hizbullah's military clout and influence within the Shiite community.
Last week, Walid Jumblatt, Druze leader and the most outspoken critic of Syria's presence here, asked, "Will Abu Hadi [Nasrallah] join us in the path for democratic and free national independence? Let there be a dialogue, and I think he alone deserves dialogue."
Complicating the process, however, is the fact that Hizbullah was singled out - at least tacitly - in UN Resolution 1559 last September. The resolution calls on Syria to withdraw from Lebanon and cease interference in Lebanese affairs. But it also calls for "the disbanding and disarmament of all Lebanese and non-Lebanese militias" - an unmistakable reference to Hizbullah and Palestinian groups.
Many in the Lebanese opposition see Resolution 1559's reference to Hizbullah as an unnecessary distraction to the resolution's broader goal of removing Syrian forces from Lebanon.
"The resolution should be about Lebanese sovereignty and a Syrian withdrawal. Mentioning Hizbullah has pushed [the group] into the corner," says Chibli Mallat, professor of international law at Beirut's St. Joseph University.
Still, Hizbullah's relationship with Syria is one of shared anti-Israeli interests rather than ideology, analysts say. The pan-Islamic Hizbullah has little in common with the secular ideology of Syria's ruling Baath Party.
And over the years, Hizbullah has earned a reputation for pragmatism. "Hizbullah is wise enough to know that it cannot opt for war," says Farid Khazen, professor of politics at the American University of Beirut. "It will be a negotiated settlement like the disbanding of the other militias."
Many analysts believe there is room for compromise. Nassib Lahoud, an opposition member of parliament, proposes holding the resistance as a "strategic reserve" until the conclusion of the Middle East peace process.
"Arrangements should be reached over Hizbullah's arms without a total dismantlement," he says. "This idea is a good step in the right direction and should satisfy Lebanese concerns and hopefully would be acceptable to the international community."
Not all opposition figures agree. "If Hizbullah wants to be a political party, that's fine. But no more militia," says Gibran Tueni, editor of An Nahar.
But Timur Goksel, a former senior adviser to the UN peacekeeping force in south Lebanon, says that forceful dismantlement would be a "recipe for disaster."
"It has to be a voluntary move by Hizbullah," he says. "Nobody is going to use force to disarm Hizbullah, because it could rip the country apart."
Hizbullah's leadership, he says, will have to deal not only with external pressure, but also appease internal dissent.
"It's going to be a risky move by the Hizbullah leadership, and they are going to have to prepare the ground for it for very carefully," he says.