Affordability will be a deciding factor in the U.S. Air Force's drive to develop a new long-range bomber, the top general in the service said on Thursday, underscoring that he was not looking for an extravagant design.

Air Force Chief of Staff General Norton Schwartz said it was critical that the military and industry come up with an airplane design that was affordable enough to be built in significant numbers and could be ready for delivery in the mid-2020s.

He said the Air Force wanted to avoid a repeat of its experience with the bat-wing B-2 stealth bomber built by Northrop Grumman Corp. .

The Air Force initially planned to build 131 of the long-range heavy B-2 bombers, but high development and operational costs, coupled with the end of the Cold War pared the order to just 21 planes -- each estimated to cost about $2 billion.

We are not going to do the B-2 again. That is not in the cards, Schwartz said after a speech hosted by the Center for Strategic and International Studies, a Washington think tank.

Northrop, Boeing Co and Lockheed Martin are eyeing possible bids for the new long-range bomber, one of few new development programs that the Pentagon is committing to funding even as it starts to cuts $487 billion from its planned spending over the next decade.

Schwartz said the Air Force had learned its lesson on the B-2 bomber program. We are going to make our best effort to not overdesign an airplane, he said, noting that the bomber would have to meet certain needs, including interfacing with existing spy planes, electronic warfare platforms and other sensors.

We are not intent on delivering a capability that is extravagant, that is excess to our absolute needs, he said, adding that the new bomber could be improved over time.

Rebecca Grant, an aviation expert who released a report on the new stealth bomber this week, said the Pentagon's decisive commitment to proceeding with a new bomber marked a huge change after years of discussion about a family of long-range strike capabilities that could d have included cruise missiles, intercontinental ballistic missiles and unmanned planes.

In the report, she said the shift made sense given the Pentagon's pivot toward the Asia Pacific region, and noted that several events during 2011 had underscored the importance of long-range strike weapons, including the use of B-2 bombers to hit hardened aircraft shelters in Libya.

B-2 bombers also stood ready as part of a back-up plan for the attack that killed Osama bin Laden in April, she said.

She acknowledge budget constraints, but said she believed industry could design an aircraft that would at least have super sonic dash speeds. Stealth was a given these days, but many other capabilities would be integrated on the new bomber.

Experts are calling for a fleet of 200 new bombers, but some wonder if the Pentagon can afford that many new aircraft at a time when defense spending is being cut sharply.

Grant argued in the report that the cost of developing a new bomber would be substantial, the Pentagon eyeing a price per plane of around $550 million.

But that was in line with other acquisition programs, including a $35 billion program to build new refueling tankers based on Boeing's commercial 767 airliner, and well below the amount likely needed for development of a new nuclear submarine.

The cost of the new bomber program would not be certain until the Pentagon picked a design and set yearly quantities, probably sometime after 2018, Grant wrote in the report.

(Reporting By Andrea Shalal-Esa; Editing by Bernard Orr)

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