Hezbollah, the militant Shiite group, quickly sought to assure the Lebanese government that it was not responsible for the two Katyusha rockets that wounded two people in the Israeli town of Nahariya, despite its leaders harsh words for Israel in recent days.

But the incident added to existing anxieties in Lebanon and once again illustrated the precariousness of the truce along Israel’s northern border.

Several armed Palestinian factions have the capability to fire rockets and operate outside the control of either Hezbollah or the Lebanese government. And rank-and-file members of Hezbollah and allied Shiite militias have been agitating for Lebanese fighters to open up a northern campaign in response to Israel’s Gaza campaign.

"We want more fire. We want the order to attack Israel directly," said a burly young man who only gave his first name, Rabih, during a speech by the Hezbollah leader, Sayyed Hassan Nasrallah, on Wednesday in southern Beirut. "We’d like to start a war with Israel today. We’ve got to crush Israel.

On Thursday morning, Israel said it fired five shells in a measured response to the rocket attack, and two hours later reported another series of rockets fired, which proved to be a false alarm.

Israel, the Lebanese government and Hezbollah all made moves that seemed calculated to preserve stability along the border. The Lebanese prime minister and several cabinet members condemned the attack, and the lone Hezbollah minister, Mohammed Fneish, distanced his party from the action.

“When Hezbollah does something, it announces it and has no problem doing so," Mr. Fneish told reporters before entering a cabinet meeting.

Hezbollah has been trying to maintain a delicate balance.

To its followers on the street, the leadership has trumpeted Hezbollah’s unyielding resistance to Israel and solidarity with Hamas. To the Lebanese government, it has signaled that it will not pull the country into a full-on war with Israel.

In his most recent speech, Mr. Nasrallah warned his supporters to be ready for any contingency involving Israel.

"We are not afraid of your planes or your threats we and are ready for any aggression," Mr. Nasrallah said, addressing the Israeli prime minister, Ehud Olmert. "If they came to our towns and homes, the Zionist will discover that their war in July 2006 was a picnic compared to what we have prepared for them."

Hezbollah has largely restrained its fighters since the July 2006 war. Palestinian factions operating in southern Lebanon have on occasion broken the calm along Israel’s northern border, including an incident on Dec. 25 when the Lebanese army discovered a battery of rockets aimed at Israel and attached to a timer. Authorities in Lebanon blamed that incident on Palestinian militants.

There are several small Palestinian factions that operate in southern Lebanon and have the capacity to fire rockets into Israel. The leaders of Hamas and Fatah in Lebanon both quickly condemned Thursday’s rocket attacks, saying they did not want implicate the Lebanese state in a Palestinian conflict with Israel.

But an official from one of the more prominent and militant factions, the Popular Front for the Liberation of Palestine-General Command, did not deny responsibility for the attack.

"Don’t be surprised to see more rockets launched into northern Israel," said Anwar Raja, a spokesman for the group. "It’s a normal response to Israel’s brutal aggression."

Hezbollah operatives in the south may have turned a blind eye to a Palestinian faction that set up the rockets, said Timur Goksel, a professor and former United Nations official in Lebanon, who is a close observer of Hezbollah.

"Most Palestinian factions here are careful not to antagonize the Lebanese, but there are some who will do anything to show their solidarity with Gaza," Mr. Goksel said.

Observers and some Hezbollah supporters in Lebanon said that Hezbollah would enter the war only if Hamas was on the verge of complete defeat.

"It’s a sensitive situation for Hezbollah," Mr. Goksel said. "There’s a lot of grassroots pressure on them to act, but I think they’ll do the smart thing and exhibit restraint."

The Lebanese army and United Nations peacekeepers said Thursday they had stepped up patrols along the Israeli border. But many in Lebanon still worry that a small spark could rekindle hostilities between Hezbollah and Israel.

"Lebanon does not want another war. We must remain vigilant not to be dragged into another conflict," Lebanese information minister Tarek Mitri told reporters this week.

Ultimately, though, it is Hezbollah and its powerful militia that holds the cards in Lebanon; the Shiite party entered the 2006 war with Israel over the objections of the western-allied government.

"The resistance stands ready to strike at any minute," said Ahmed Haidar, an operative of the Shiite group Amal, whose militia and political bloc are closely allied to Hezbollah. "We believe that Israel might attack us at any minute, because that’s what Israel does to the Arabs."