The parliament speaker, a close ally of Hezbollah who was supposed to meet with Blair, left town in an apparent snub to the first British leader to visit Lebanon.
The country's most senior Shiite Muslim cleric said he held Blair responsible for the deaths of hundreds of Lebanese civilians during the 34-day war because Britain supported the United States in refusing to demand a quick cease-fire.
While Lebanese Prime Minister Fuad Saniora greeted Blair at the airport, hundreds of demonstrators gathered in central Beirut. The two leaders road into the city in a 22-vehicle motorcade, with hundreds of security forces guarding the route.
"Blair, you are not welcome in Lebanon," read a banner carried by protesters. "In the name of the Lebanese people: Thank you for destroying our homes, neighborhoods and memories."
Grand Ayatollah Mohammed Hussein Fadlallah said Sunday that Blair was a "killer of children, women and the elderly" and should be declared "persona non grata" in Lebanon.
The As-Safir daily described Blair as "the ugly Briton" and called his invitation to Beirut "a political mistake that could have been avoided." Another daily, Al Balad, warned riots might erupt.
Hundreds of Lebanese troops and police, backed by armored carriers, sealed off the main squares in downtown Beirut, setting up roadblocks to keep demonstrators and cars away.
A protest had been planned in front of the government's seat, but the police authorized it about half a mile away, beyond the sight of Blair's meeting with Saniora.
Blair helped nudge forward stalled Israeli-Palestinian peace during talks in Jerusalem and the West Bank city of Ramallah over the weekend.
He had planned to meet with Lebanese Parliament Speaker Nabih Berri before heading home later Monday. But Berri, a Shiite, left the country two days earlier on a private visit, an apparent snub to Blair.
Blair was not expected to meet with President Emile Lahoud, a pro-Syrian whom Western nations have refused to deal with in the last year. Syria is accused of being one of Hezbollah's chief backers, along with Iran.
Blair particularly wants to show support for Saniora and the U.N. cease-fire resolution, said a spokesman for British prime minister, speaking on condition of anonymity in keeping with policy. He said Blair had been willing to meet with two Hezbollah members of Lebanon's Cabinet, but both had chosen not to attend talks.
"What people should not do is make the mistake of saying that Hezbollah equals Lebanon," the spokesman said. He said Blair would not be surprised to be greeted by demonstrators because of the anger over the war.
Blair is the first British prime minister to visit Lebanon, and the second Western leader to come to Beirut since fighting erupted in July. France's premier traveled to Beirut during the fighting.
Blair's handling of the Israel-Hezbollah added to his political troubles at home. His refusal to break with Bush and call for an immediate cease-fire helped drive a rebellion within his Labour Party, culminating in his reluctant announcement Thursday that he would resign within a year.
Many Labour loyalists saw Blair's stance as a tacit endorsement of Israel's offensive, which killed more than 850 people in Lebanon, most of them civilians. Blair says it took time to craft a peace plan that would hold and argued that a quick cease-fire could have collapsed.
In Israel and the West Bank, Blair got a warmer reception, though a handful of protesters demonstrated outside his meeting in Ramallah with Palestinian President Mahmoud Abbas.
After meeting with Blair, both Abbas and Israeli Prime Minister Ehud Olmert said they would hold talks, a small step toward reviving peace efforts that have been paralyzed for months.
Blair also tried to draw Hamas into peace efforts, but the militant group, which controls the Palestinian government, rejected his condition that it first renounce violence and recognize Israel.
Despite Hamas' tough stance, the readiness of Olmert and Abbas to meet without conditions was the first sign of progress toward peace in months.
Meanwhile, Blair was quoted as saying in an interview published Monday that ignoring Iran's threats to destroy Israel, especially when it appears to be intent on developing nuclear weapons, could prove to be a historic mistake.
Blair, in an interview with the Israeli daily Haaretz newspaper, said such neglect would compare to the Western appeasement policy that failed to rein in Adolf Hitler in the 1930s.