No, I think we can quite safely say that the US government had nothing to do with the 911 terrorist attacks. It's very hard to believe that a state would murder 3,000 of its own people to justify a war in the Middle East.
The conspiracy theories that relate to the US government's involvement in the attacks are based upon very ropey evidence - which has been cobbled together in the interest of people trying to discredit the US government. Now, I'm not a fan of George W. Bush or the Republican party, but not for one minute do I think they would orchestrate an attack on their own country.
However, I do think the US government's actions certainly contributed to the attack. Security was too lax upon domestic flights, and anti-terrorism agencies did not pick up the terrorists whilst they were operating in the country. Also, years of aggressive American foreign policies in Middle Eastern countries contributed to the attack.
