BEIRUT — With memories of a destructive war 29 months ago still vivid, Lebanese political leaders for days have assured their constituents that the powerful Shiite Muslim militant organization Hezbollah wouldn't dare enter the fray between its fellow Islamists of Hamas and the groups' longtime common enemy, Israel.
But as the Israeli offensive against Hamas in the Gaza Strip continues to rage, many are beginning to wonder what it would take for Hezbollah to open a new military front in order to distract Israel and ease the pressure on Hamas to the south.
That question took on a fresh urgency this morning when three to five rockets fired from Lebanon struck northern Israel, causing minor injuries five miles from the frontier, and Israel responded with its own barrage of rockets, Israeli and Lebanese officials said.
There was no claim of responsibility for the initial attack, and the short-range Katyusha rockets could have been fired by one of the Lebanese-based Palestinian groups with no affiliation to Hezbollah. Palestinian militants in Lebanon fired two rockets into northern Israel in June 2007.
For now, most Lebanese analysts and political leaders say Hezbollah wouldn't risk its domestic popularity ahead of critical May parliamentary elections it believes will solidify its power. Lebanese Information Minister Tarek Mitri told reporters Monday of a nationwide "sense of not wanting to be drawn into this" conflict.
"Expressing solidarity with Gaza," he said, "does not mean wanting to provoke an Israeli attack on Lebanon, or giving any pretext for that."
So far, Hezbollah leader Sheik Hassan Nasrallah has given no indication that his militia, replenished with rockets from Iran and Syria since its summer 2006 war with Israel, would launch or provoke a new conflict. A Hezbollah Cabinet minister even agreed last week to a Lebanese government statement pledging to keep the politically divided country from being drawn into the conflict.
But on Wednesday, Nasrallah did warn of dire consequences if Israel struck first.
"We are ready for any aggression," he told followers chanting "Death to Israel!" at annual Ashura religious ceremonies. "If you come to our villages, our lands, our neighborhoods, you Zionists will discover that the July  war was nothing compared with what you'll face this time."
Almost all observers acknowledge that Hezbollah's reluctance to stage a military operation could change dramatically if the fighting in Gaza, which began 12 days ago, continues to stoke passions for weeks longer.
"There comes a point when duty becomes a factor," said a Western diplomat in the Middle East, speaking on condition of anonymity. "There's more a mounting pressure from the Arab street, and Hezbollah are the leaders of the Arab street."
Mitri, the Lebanese government official, said, "The more there is a delay in acting, the greater is the anger and the more significant is the radicalization of hearts and minds, the more there is a chance of spillover of the violence."
Hezbollah might also reconsider its militarily passive stance, analysts say, if it feared Hamas was about to suffer a catastrophic defeat that would irreparably harm the Palestinian national cause and change the region's balance of power.
"The likelihood for opening up a front depends entirely on Hamas' performance," said Amal Saad-Ghorayeb, a Lebanese scholar who has written about Hezbollah and Iran. "If Hamas is defeated, the Palestinian cause would be in serious jeopardy. On ideological or strategic grounds, [Hezbollah] cannot allow Hamas to be toppled."
The mountain ridges of southern Lebanon, long a staging ground for Arab attacks into Israel, were largely under the control of Hezbollah and allied militias during the 2006 war with Israel. Since that conflict, the Lebanese army and a bolstered United Nations peacekeeping force of about 13,000 international troops patrol the area south of Lebanon's Litani River, making it tougher for Hezbollah to launch rockets into northern Israel. U.N. officials describe the situation in the south so far as stable.
But neither the U.N. force, known as UNIFIL, nor the Lebanese army is taking chances. They've stepped up patrols in recent weeks, largely in response to the discovery late last month of a cache of Katyusha rockets aimed at Israel.
"The regional situation might change at any moment," said a Lebanese military official, speaking on condition of anonymity. "The Lebanese army, along with UNIFIL, have taken all the necessary measures to deal with every step at a time."
The Israeli military has deployed reservists to the north and warned against attacks by Hezbollah or its allies. "I can only estimate that Hezbollah, along with the Iranians, are concerned by the massive blow Hamas suffered, fearing it might mark the first domino to knock down the narrative of resistance," Israel Defense Forces spokesman Brig. Gen. Avi Benayahu told Israel's Army Radio on Monday.