* Defense secretary questioned need for so many carriers

* Marines push back on need for amphibious operations

* Gates to discuss political will, defense budget

WASHINGTON, May 6 (Reuters) - The U.S. Navy told Congress it wants to keep 11 aircraft carriers through 2045, just days after Defense Secretary Robert Gates called into question the need for that many.

“The Navy remains firmly committed to maintaining a force of 11 carriers for the next three decades,” Sean Stackley, the service’s warship buyer, told the Senate Armed Services Seapower subcommittee on Thursday.

The 11-carrier force structure is based on “world-wide presence requirements, surge availability, training and exercise, and maintenance” needs, he said in an opening statement.

Gates stirred the waters on Monday with a speech in which he asked whether the United States could afford “a Navy that relies on 3- to 6-billion-dollar destroyers, along with 7-billion-dollar submarines and 11-billion-dollar carriers.”

He cited both the “massive over-match” enjoyed by the United States in projecting power across the oceans as well as potential foes’ growing anti-ship know-how, including cruise and ballistic missiles that could strike from over the horizon.

“Do we really need 11 carrier strike groups for another 30 years when no other country has more than one?” Gates asked the annual conference of the Navy League, a supporters’ group.

In addition, he circled back to his doubts, first voiced publicly last April, about amphibious warfare. He repeated questions about a projected $13.2 billion Expeditionary Fighting Vehicle program for the Marine Corps.

The Commandant, General James Conway, has said it is "an absolute critical requirement" for the Marines. The program is led by General Dynamics Corp GD.N.

Northrop Grumman Corp NOC.N and Lockheed Martin Corp LMT.N are other big Navy suppliers.

The Navy and Marine Corps have determined they can make do with no fewer than 33 amphibious warfare ships, Stackley, the assistant Navy secretary for research, development and acquisition, testified Thursday.

Lieutenant General George Flynn, the deputy Marine commandant for combat development and integration who also testified, said 33 such ships represented a “limit in acceptable risk” for two Marine expeditionary brigades to punch their way through enemy shores.

“Now after eight years of conflict on land, it is important that we challenge conventional thought with regard to the utility of sea-based forces,” Flynn had said Tuesday at a roll-out of the latest prototype of the Marines’ new $16 million-plus craft for hurtling from ship to shore and inland.

Senator James Webb, a panel member who was President Ronald Reagan’s Navy secretary, shot back at Gates during the hearing.

“I think it would be a very serious mistake to cut back on the defense budget in order to fund ground forces that are in Iraq and Afghanistan, hopefully temporarily,” the Virginia Democrat said, “at the expense of these vital shipbuilding programs that take years and years to put into place.”

Gates, in his remarks on Monday, said the military risked creating a gap “between the capabilities that we are pursuing and those that are actually needed in the world of tomorrow.”

The defense secretary is to speak about “political will and the defense budget” on Saturday. He will be visiting the presidential library in Kansas of Dwight D. Eisenhower, who warned against a “military-industrial complex” in his farewell speech of Jan. 17, 1961. (Reporting by Jim Wolf; Editing by Gary Hill)