BEIRUT — Over one million opposition backers chanted “Freedom, Sovereignty, Independence” and unfurled a huge Lebanese flag in central Beirut yesterday, throwing the biggest protest yet in the opposition’s duel of street rallies with supporters of Syria and the Lebanese government.

Crowds of men, women and children flooded Martyrs’ Square, spilling over into nearby streets, while more from across the country packed roads into Beirut — responding to opposition calls to mark a month since the assassination of former Prime Minister Rafik Hariri. His slaying sparked a series of protests against Syria, the dominant power in Lebanon.

“We are coming to liberate our country. We are coming to demand the truth,” said Fatma Trad, a veiled Sunni woman who traveled from the remote region of Dinniyeh in northern Lebanon to take part.

The protest was heavily mixed, reflecting Lebanon’s religious diversity. Druse descended from the Chouf and Aley mountains east and southeast of Beirut and Christians arrived from the heartland in the northeast. There was a big turnout of Sunni Muslims, including many who bused into the capital from northern Lebanon’s Tripoli, Dinniyeh and Akkar regions, plus from Hariri’s hometown, Sidon, in southern Lebanon and Beirut itself.

The protest, potentially the biggest in Lebanon’s history, easily exceeded the pro-government rally of some 500,000 held last week by Hezbollah. That show of strength forced the opposition to act to regain its momentum. Police officers privately estimated yesterday’s crowd at over one million people, but refused to speak publicly because of the sensitivity of the issue as it was an opposition rally.

A long line of people in Martyrs’ Square carried a 100-meter white-and-red Lebanese flag with the distinct green cedar tree in the middle, shaking it and demanding Syria’s withdrawal. Another banner read “Syria out, no half measures,” apparently borrowing from US President George W. Bush’s “half measure” description of Syria’s gradual withdrawal.

Many protesters waved Lebanese flags and released thousands of red and white balloons into the sky above the teeming crowd. Thousands wore the red and white scarves that have come to symbolize the country’s anti-Syrian movement, which the State Department has dubbed the “Cedar Revolution.”

Brass bands playing patriotic and national folk songs and Lebanon’s national anthem were regularly drowned out by deafening chants from the crowd.

Unlike the Hezbollah rally, there were no references to the West or the United States, which has been leading the international drive to get the Syrians out of Lebanon.

Syria’s military withdrawal continued yesterday, with intelligence agents closing offices in the northern towns of Amyoun and Deir Ammar, on the coastal road between the port city of Tripoli and the Syrian border.

Intelligence agents dismantled two checkpoints in the Akkar area. In all, more than 70 intelligence agents left — destination unknown, but believed to be northern Syria.

Most intelligence offices, the widely resented arm through which Syria has controlled many aspects of Lebanese life, remained in northern and central Lebanon after Syrian troops moved east, closer to the Syrian border.

Last week, intelligence officers left two central towns, Aley and Bhamdoun, and headed to the Syrian-controlled areas of eastern Lebanon. The redeployment is the first stage of what Damascus says will be a full withdrawal, though it has not given a timetable.