US government experts also believe that the likelihood of an attack using chemical, biological, atomic or radiological weapons over the next year is not high.
Robert Cardillo, deputy director of US National Intelligence, described the assessments at a press conference.
The meeting with journalists was billed as an opportunity for government experts to voice their views on al Qaeda's potency a year after the killing of Osama bin Laden.
Mr Cardillo said the al Qaeda "core" organisation that bin Laden created had suffered strategic setbacks due to the outbreak of "Arab Spring" protests.
These, and rebellions in Islamic countries, had not spread great sympathy for al Qaeda's hardline and violent brand of Islam, Mr Cardillo said.
An unnamed counterterrorism official said it was clear there had been "progress towards defeating al Qaeda the organisation".
While it was "too soon to declare victory", the official said "some could argue that the organisation that brought us 9/11 is essentially gone".
More worrying to US counterterrorism officials and their allies abroad is the possibility of home-grown extremists, or "lone wolves".
The officials said that four al Qaeda spinoffs or affiliates still posed threats of greater or lesser degree to US interests.
Most deadly, the officials said, was Yemen-based al Qaeda in the Arabian Peninsula (AQAP).
Officials believe this group was behind unsuccessful but imaginative attempts to attack continental US targets over the last 18 months.
One of the attempts used a bomb stashed in an air passenger's underwear and another saw explosives concealed in photocopier ink cartridges.
Al Qaeda in Iraq, which arose in the wake of the 2003 US invasion to oust Saddam Hussein, also remains a potentially lethal presence in that country, the officials said.