WASHINGTON, Oct 11 (Reuters) - President George W. Bush on Wednesday described as not credible a study showing 655,000 Iraqis had died in violence since the U.S.-led invasion of Iraq. "I don't consider it a credible report," Bush said of a study by a team of American and Iraqi public health experts that calculated about 655,000 Iraqis had died as a result of the March 2003 U.S.-led invasion and subsequent violence.