The document says the failure to kill or capture the al-Qaeda leader in the mountains of Tora Bora in Afghanistan at his most vulnerable in December 2001 has had lasting consequences.
Bin Laden's escape laid the foundation for the reinvigorated Afghan insurgency and inflamed the internal strife now endangering Pakistan, it says.
The Senate Foreign Relations Committee's Democratic majority prepared the report at the request of the chairman, Sen John Kerry, as President Barack Obama prepares to boost U.S. troops in Afghanistan.
Mr Kerry, the 2004 Democratic presidential candidate, has long argued the Bush administration missed a chance to get the al-Qaeda leader and top deputies when they were holed up in the forbidding mountainous area of eastern Afghanistan only three months after the Sept. 11, 2001, terrorist attacks.
The report puts part of the blame for the state of the war today on military leaders under former President George W Bush, specifically Donald Rumsfeld as defence secretary and his top military commander, Tommy Franks.
"Removing the al-Qaeda leader from the battlefield eight years ago would not have eliminated the worldwide extremist threat," the report said. "But the decisions that opened the door for his escape to Pakistan allowed bin Laden to emerge as a potent symbolic figure who continues to attract a steady flow of money and inspire fanatics worldwide.
"The failure to finish the job represents a lost opportunity that forever altered the course of the conflict in Afghanistan and the future of international terrorism."
The report states categorically that bin Laden was hiding in Tora Bora when the U.S. had the means to mount a rapid assault with several thousand troops at least.
It says that a review of existing literature, unclassified government records and interviews with central participants "removes any lingering doubts and makes it clear that Osama bin Laden was within our grasp at Tora Bora."
On or about Dec 16, 2001, Bin Laden and bodyguards "walked unmolested out of Tora Bora and disappeared into Pakistan's unregulated tribal area," where he is still believed to be based, the report says.
Instead of a massive attack, fewer than 100 US commandos, working with Afghan militias, tried to capitalise on air strikes and track down their prey.
"The vast array of American military power, from sniper teams to the most mobile divisions of the Marine Corps and the Army, was kept on the sidelines," the report said.
At the time, Mr Rumsfeld expressed concern that a large US troop presence might fuel a backlash and he and some others said the evidence was not conclusive about bin Laden's location. (London Telegraph, 11.29.2009) http://www.telegraph.co.uk/news/worldnews/asia/afghanistan/6683160/Osama-bin-Laden-was-within-reach-of-US-troops-in-Afghanistan.html