Plenty of them, yes.

From the Gulf of Tonkin; to "weapons of mass destruction"; to Iran Contra and the allegations the US knew about (and helped) Saddam use chemical weapons on Iran (claimed to be equivalent to a conspiracy theory at the time, turns out it was completely true).

Echelon, Carnivore and the NSA spying on everybody (including Americans)? Conspiracy theories. Joe Nacchio and Qwest? Conspiracy theory.

The US involved over the decades in toppling governments in South America? The US Govt. denies it to this day, just a bunch of conspiracy theories.

All of this is of course due to the Politik exercising the ability to keep secrets. Such agency is exactly the environment in which one conspires; without walls erected to maintain a mystery, it is near impossible to hate in peace.