Halutz has been under pressure to step down ever since the end of the 34-day war. His resignation is an indirect blow to Prime Minister Ehud Olmert, himself the target of stinging criticism over his handling of the war — and his decision to launch it in the first place.
A few hours earlier, the Justice Ministry ordered police to launch a criminal investigation of Olmert's role in the 2005 government sale of one of Israel's largest banks, further eroding his public standing. Last week a newspaper poll showed his public approval rating standing at just 14 percent — largely a result of the war.
Israel launched a full-scale assault on Lebanese Hezbollah guerrillas after they captured two soldiers and killed three others in a cross-border raid July 12, but the operation failed in its main goals — defeating Hezbollah and bringing the captured soldiers home.
The military spokesman's office said Halutz tendered his letter of resignation to Olmert and Defense Minister Amir Peretz, who also faces widespread criticism of his role in the war.
Army Radio reported that Halutz said in the letter that he was taking responsibility for the outcome of the war.
"For me the concept of responsibility is everything," Halutz wrote, according to Army Radio.
In its announcement of Halutz's resignation, the military spokesman's office said Halutz had decided to resign after dozens of military inquiries into various aspects of the war. "Now that this process has completed, the chief of staff has asked to resign immediately," the brief statement said.
None of the inquiries concluded that he should step aside or be replaced.
The spokesman's office said both Olmert and Peretz have to accept the resignation before it can go into effect.
There were no immediate comments from the offices of Olmert or Peretz, who have also been assailed for their conduct during Israel's largest military operation since 1982.
The fighting left more than 1,000 people dead on both sides, according to the U.N., Israeli and Lebanese officials. Lebanon's Higher Relief Council, a government group, says the majority of those killed were Lebanese civilians. UNICEF said that about a third of them were children.
The fatalities included 159 in Israel, including 39 civilians killed in rocket attacks.
Hezbollah fired about 4,000 rockets at Israel during the war, which ended Aug. 14 with a U.N. Security Council resolution that posted a beefed-up peacekeeping force in southern Lebanon.
Israel claims 600 Hezbollah fighters were killed, but that figure has not been substantiated. Hezbollah claims that only 250 of its fighters were killed.
Halutz resigned before a government-appointed committee, which has the power to call on him to step aside, could issue its findings on the war.
The chorus of calls for his resignation swelled in the immediate aftermath of the war, ebbed, then surged again months later after an internal panel submitted a scathing report on the raid that touched off the fighting.
More recently, an inquiry by a former chief of staff found that the war's goals were vaguely defined, and that there was faulty work in command centers.
Reserves generals have criticized Halutz, a former air force chief, for focusing too much on aerial bombardments and not enough on ground operations.
Critics have also questioned his decision to send troops on a last-minute push in which more than 30 soldiers died.
Reports from the battlefield, meanwhile, described a military command that sent troops out to battle inadequately armed, clothed and fed.
Maj. Gen. Moshe Kaplinsky, who was dispatched to the Lebanon front to assume command during the war, told Israel TV last week that he would be a candidate for chief of staff after Halutz leaves. Kaplinski is currently serving as deputy chief of staff.
Another candidate is Maj. Gen. Gabi Ashkenazi, who has served in several command positions.
The war has cost two other career soldiers their jobs.
Brig. Gen. Gal Hirsch resigned after being singled out for criticism because he was in charge of the unit along the Israel-Lebanon border that was attacked in the July 12 raid.
Maj. Gen. Udi Adam, who headed the army's northern command, including the Lebanon front, resigned a month after the war ended. Halutz shunted him aside and effectively replaced him with Kaplinsky while the fighting was still going on.
Also, Halutz fired a third general who publicly criticized the Lebanon war and government policy.
Halutz stepped down after less than two years on the job. His entry into the post on June 1, 2005, marked the first time an air force chief commanded the entire military force.
Halutz was a controversial figure in some quarters even before he took over as chief of staff. Complaints have been filed against him abroad in connection with his 2001 decision, as air force commander, to drop a one-ton bomb on a Gaza Strip home in a 2002 airstrike that killed a Palestinian militant leader and 14 others, nine of them children.
He is not the first military chief to abruptly have his tenure ended. Lt. Gen. David Elazar was fired in 1974 after the surprise attack on Israel by Egypt and Syria that began the 1973 war.