The U.S. Navy would really like to drop from twelve to ten carriers, and save a lot of money, mainly on manpower. Each sailor costs over $100,000 a year to maintain, and a carrier task force contains over 6,000 sailors. The money saved from eliminating two carrier task forces would be used for investment in the new missions. For example, there is a need for smaller vessels for coastal and riverine operations, for naval infantry, for more civil affairs troops, for more special operations support, and so on. The navy believes that if it doesn't become more active in these other missions, it will become irrelevant in the public's mind. Most people, including members of Congress and even the President's inner circle, haven't a clue as to what the navy's been doing in the war on terror. There is also a general ignorance of the navy lack of appropriate equipment and capabilities to be more useful in the war on terror. Thus the need to cut two carriers, and invest in things are needed to be more useful in the war on terror.
Ten carriers would still be sufficient for a major contingency or two (like China and Iran). Unfortunately, the Navy's staunchest "friends" -- the veterans, the Navy League, the slovenly shipbuilders - all would like to keep building as if the Imperial Japanese Navy were still out there. This "carrier lobby" has been actively blocking navy attempts to restructure the fleet to better deal with new tasks. It's another case of the "Industrial-Congressional Complex" pushing its own agenda at the expense of the troops and the country.