Robert Gates assumed the helm at the Defense Department on Monday, warning in his first public remarks as defense secretary that failure in Iraq would be a "calamity" that would haunt the United States for years. The former CIA chief pledged to give President George W. Bush his honest advice on the costly and unpopular war, and said he would go to Iraq soon to see what US commanders believe should be done to quell the growing violence. "All of us want to find a way to bring America's sons and daughters home again," Gates, 63, said after taking the oath of office as defense secretary from Vice President Dick Cheney at a Pentagon ceremony. "But as the president has made clear, we simply cannot afford to fail in the Middle East. Failure in Iraq at this juncture would be a calamity that would haunt our nation, impair our credibility, and endanger Americans for decades to come." He takes office as Bush conducts a wide-ranging review of his approach to the 3 1/2 year-old Iraq conflict. The fighting, teetering on the edge of a civil war between sects, has seen more than 2,940 Americans die at a cost to U.S. taxpayers exceeding $300 billion (â‚¬229.1 billion) Officials say the options Bush is studying run from a short-term buildup of thousands of more troops to a pullback of US combat units so they can focus on training Iraqis and hunting terrorists. Bush said last week that he would wait until January to announce his new strategy, to give Gates a chance to offer advice. Gates said he wants to hear the views of US commanders on how to improve the situation, "unvarnished and straight from the shoulder." The remarks seemed to contrast with critics' complaints that the man he replaced, Donald H. Rumsfeld, did not listen enough to the advice of the military's top officers. Bush called Gates "the right man" for the multiple challenges of Iraq and the global war on terrorism. "We are a nation at war," Bush said. "And I rely on our secretary of defense to provide me with the best possible advice and to help direct our nation's armed force as they engage the enemies of freedom around the world. Bob Gates is the right man to take on these challenges. He'll be an outstanding leader for our men and women in uniform." Gates formally assumed the job earlier Monday in a private swearing-in ceremony at the White House, replacing Donald H. Rumsfeld. He took office more than month after President Bush announced he was switching Pentagon chiefs, saying he wanted "fresh perspective" on the widely unpopular and costly war and acknowledging the current approach was not working well enough. Rumsfeld was a chief architect of the war strategy and still defends the decision to invade in March 2003. "You have asked for my candor and my honest counsel at this critical moment in our nation's history, and you will get both," Gates said. He said that since his Senate confirmation earlier this month he has participated in meetings on Iraq at the White House, received briefings at the Pentagon and held in-depth discussions with the president on ways ahead in Iraq. Besides the wars in Iraq and Afghanistan, Gates faces other immediate challenges. One is the Army's proposal that it be allowed to grow by tens of thousands of soldiers, given the strains it is enduring from the two wars. Rumsfeld had resisted increasing the size of the Army or the Marine Corps; Gates' view is unknown. It is not yet clear whether Gates intends to immediately shake up the Pentagon by firing generals or replacing senior civilian officials. He has asked Gordon England, the deputy defense secretary, to remain, but some have already announced their departures, including the top intelligence official, Stephen Cambone. In his remarks Monday, Gates said he looked forward to working with Gen. Peter Pace, chairman of the Joint Chiefs of Staff, as well as the service chiefs and civilian service secretaries. Gates, who had been president of Texas A&M University since 2002, completed his tenure over the weekend by attending three commencement ceremonies on the campus. At his confirmation hearing, Gates won plaudits for his candor, especially for acknowledging the U.S. was not winning in Iraq. That contrasted with Bush's remark at an Oct. 25 news conference that, "Absolutely, we're winning."