ST. PETERSBURG, Russia — World leaders tore up a carefully prepared summit agenda Saturday and turned their attention to a growing crisis in the Middle East, hoping to reach common ground on ways to stop the fighting.

Russian President Vladimir Putin said he was grateful that President Bush came early for bilateral talks that Putin said would allow them to synchronize their watches on a host of world crises and provide a "boost to the G-8 summit."

Putin designed this year's Group of Eight economic summit, the first to be held in Russia, to showcase his country's re-emergence on the world stage after a devastating economic collapse in 1998. He had hoped to focus on energy security, the fight against infectious diseases and education.

But officials were quickly clearing discussion time to address a new explosion of violence in the Middle East. The G-8 countries — the United States, Russia, Japan, Germany, Britain, France, Italy and Canada — were expected to issue a joint declaration on the Lebanon crisis but drafters of the document faced the need of dealing with sharp differences between the United States and the other countries over how to proceed.

Israel's war planes began striking Lebanon after Hezbollah guerrillas captured two Israeli soldiers and killed eight others Wednesday in a cross-border raid into Israel. Since Wednesday, Hezbollah has fired hundreds of rockets at northern Israel.

Bush said that Israel has a right to defend itself while other summit leaders have condemned what they see as an overreaction on the part of Israel that has caused dozens of civilian deaths and risked a major escalation of bloodshed in the Middle East.

The other G-8 leaders flew into St. Petersburg for three days of discussion beginning with an opulent dinner at a former czarist palace on Saturday night. Bush and the other leaders were staying in guest houses on the grounds of the Konstantin Palace on the Bay of Finland, an area that was sealed off by heavy security.

Anti-globalization protesters vowed to march in St. Petersburg despite an official ban and warnings from a top Kremlin official against violating a ban on marches. City authorities have limited the activities of protesters to a stadium in a hard-to-reach part of St. Petersburg.

In a joint news conference with Putin, Bush said Saturday that "all parties want the violence to stop" in Lebanon. In his comments, he blamed the Islamic militant group Hezbollah for escalating the violence.

However, Putin and other G-8 leaders have been more critical of Israel.

Putin said that while Israel's concerns about the abductions and missile strikes were justified, "the use of force should be balanced."

The sudden flare-up of violence was threatening to hijack this year's summit, which already was facing the need to address nuclear threats being posed by Iran and North Korea.

Italian Premier Romano Prodi said the "spiral of violence" in the Middle East was an indication that the situation had "regressed 20 years."

French President Jacques Chirac was even harsher in his comments about Israel, saying, "One could ask if today there is not sort of a will to destroy Lebanon, its equipment, its roads, its communications."