WASHINGTON - More than a third of Americans suspect their Government was involved in the September 11 attacks, a poll shows.

The United States Government is attacking conspiracy theories about the destruction of the World Trade Center in New York as the fifth anniversary of September 11 approaches.

According to the Scripps Howard/Ohio University poll carried out in July, more than one-third of Americans suspect officials helped in the attacks or took no action to stop them so the United States could go to war.

The State Department responded with a rebuttal of World Trade Center demolition theories and doubts about other events of the day that abound on the internet.

It listed some of the most prevalent September 11 myths, led by claims the twin towers were destroyed by secretly planted explosives, not burning passenger jets.

"This is how the collapses may have appeared to non-experts, but demolition experts point out many differences," said a department "special feature" available at USINFO

Demolition professionals always blow the bottom floors of a structure first, while the collapses began at upper levels - where the hijacked Boeing 767s hit, it said.

Nearly 3000 people were killed on September 11. The Bush Administration responded by leading an invasion of Afghanistan and, in 2003, of Iraq.

The State Department was providing "corrective information" in response to misinformation in the media and on the internet, said Joanne Moore, a department spokeswoman.

The US National Institute of Standards and Technology posted a "fact sheet" on its website responding to alternative theories about the fire and the collapse.