U.S. eyes 12 giant "bunker buster" bombs

* Bombs designed to destroy deeply-buried targets

* Could be operational by next summer

WASHINGTON, Aug 27 (Reuters) - The U.S. military wants to speed production of 10 to 12 huge “bunker buster” bombs, the Air Force said on Thursday, amid concerns over suspected underground nuclear sites in Iran and North Korea.

“These are purchases beyond just those needed to test the capability,” said Lieutenant General Mark Shackelford, the top uniformed officer dealing with Air Force weapons-buying. “In other words, (the military is seeking to) build a small inventory ... of, I believe, 10 to 12.”

The Defense Department asked Congress last month to shift $68 million in the fiscal 2009 budget to speed output of the non-nuclear, 30,000-pound Massive Ordnance Penetrator and its integration aboard a long-range bomber.

The precision-guided MOP, built by Boeing Co BA.N, is designed to destroy deeply-buried targets beyond the reach of existing bombs.

Packing more than 5,300 pounds (2,404 kilos) of explosives. it would deliver more than 10 times the explosive power of its predecessor, the 2,000-pound (907-kilo) BLU-109, according to the Pentagon’s Defense Threat Reduction Agency, which has funded and managed the weapon’s development program.

Assuming Congress approves the accelerated funding as expected, the Northrop Grumman Corp NOC.N-built radar-evading B-2 bomber, "would be capable of carrying the bomb by July 2010," Andy Bourland, an Air Force spokesman, said this month.

Shackelford, at an Air Force briefing on acquisition issues, said the next phase of work would start within the next few months provided Congress approves.

In its July 8 request to Congress, the Defense Department said the MOP was the “weapon of choice” to meet an urgent operational need cited by the U.S. Pacific Command, which takes the lead in U.S. military planning for North Korea, the Central Command, which handles Iran, as well as the Strategic Command, which deals with the long-range U.S. arsenal.

In that request, the Pentagon said it needed four of the bombs. The Air Force did not immediately respond to a question about the discrepancy between those four and the 10 to 12 mentioned by Shackelford,

The United States is leading international efforts to persuade Iran and North Korea to abandon their nuclear programs, declining to rule out possible military action.

The MOP would be about one-third heavier than the 21,000-pound (9,500 kg) GBU-43/B Massive Ordnance Air Blast bomb -- dubbed the “mother of all bombs” -- that was dropped twice in tests at a Florida range in 2003.

The 20-foot-long (6-metre) MOP is built to be dropped from either the B-52 or the B-2 “stealth” bomber. It is designed to penetrate up to 200 feet (61 metres) underground before exploding, according to an article published by the U.S. Air Force.

The suspected nuclear facilities of Iran and North Korea are believed to be largely buried underground to escape detection and boost their chances of surviving attack.

During a visit to Jerusalem in July, U.S. Defense Secretary Robert Gates sought to reassure Israel that President Barack Obama’s effort to use diplomacy to persuade Iran to give up its nuclear work was not “open-ended.”

Iran says its uranium enrichment -- a process with bomb-making potential -- is for energy only and has rejected U.S.-led demands to curb the program.

North Korea responded to new United Nations sanctions, imposed after it detonated a second nuclear device, by vowing in June to press ahead with the production of nuclear weapons and act against international efforts to isolate it. (Editing by Alan Elsner)