The US intelligence network created after the September 11, 2001 terror attacks is so unwieldly even principal actors within it are unable to grasp its size, according to a two-year probe by the Washington Post published Monday.

The newspaper's investigation found that nine years after the attacks on New York and Washington, the bureaucracy has become "so unwieldy and so secretive that no one knows how much money it costs, how many people it employs, how many programs exist within it or exactly how many agencies do the same work."

Among the findings were some 1,271 government organizations and 1,931 private companies working on counterterrorism-related programs, and 33 building complexes built or under construction to house top-secret work -- the same amount of space as nearly three Pentagons or 22 US Capitol buildings.

"There has been so much growth since 9/11 that getting your arms around that -- not just for the DNI [Director of National Intelligence], but for any individual, for the director of the CIA, for the secretary of defense -- is a challenge," Defense Secretary Robert Gates told the Post.

But interim DNI chief, David Gompert, hit back at the Post report, saying: "The reporting does not reflect the Intelligence Community we know."

While intelligence agencies "operate in an environment that limits the amount of information we can share," US agents have "thwarted attacks, and are achieving untold successes every day."

"The importance of our mission and our commitment to keeping America safe will remain steadfast, whether they are reflected in the day's news or not," he said.

Pentagon spokesman Marine Colonel David Lapan acknowledged problems in the collection and sharing of intelligence.

"We do recognize that there are probably some redundancy and inefficiencies" in the growth of the intelligence agencies since the September 11 attacks, he said.

"At the same time we are reminded that since 9/11 we have not had a sucessful major attack on the United States, so there is obviously goodness in having a robust capability," he said.

The Post investigation also maintained that the size of the bureaucracy resulted in huge waste, with homeland security and intelligence programs carried out in some 10,000 locations across the country.

Fifty-one federal and military commands located in 15 US cities are now dedicated to tracking the flow of money to and from terrorist networks, and with various agencies producing a whopping 50,000 intelligence reports each year, the volume is so large the Post said "many are routinely ignored."

Retired army lieutenant general John Vines, who was once in command of 145,000 troops in Iraq and last year tasked with reviewing the Pentagon's top secret programs, said the "complexity of this system defies description."

Vines told the Post he was "not aware of any agency with the authority, responsibility or a process in place to coordinate all these interagency and commercial activities."

The September 11 attacks involved a series of coordinated suicide attacks by the extremist Al-Qaeda network upon the United States in which almost 3,000 people died.

A total of 19 Al-Qaeda militants hijacked four commercial passenger jets that day and flew two of them into the twin towers of the World Trade Center in New York City, killing everyone on board and many more in the buildings.

A third airliner was crashed into the Pentagon building in Arlington, Virginia, and the fourth fell into a field near Shanksville, Pennsylvania.