The lineup of weapons the Pentagon has picked to fit President Barack Obama's new forward-looking defense strategy, called "Priorities for 21st Century Defense," features relics of the past.

They include the Air Force's venerable B-52 bomber, whose current model entered service shortly before Obama was born. There is the even older U-2 spy plane, which began flying in 1955 and burst into the spotlight in May 1960 when Francis Gary Powers was shot down over the Soviet Union.

When Obama went to the Pentagon on Jan. 5 to announce his new defense strategy he said that as the U.S. shifts from a decade of war in Iraq and Afghanistan it will "get rid of outdated Cold War-era systems." He was not specific. But when the first details of the Pentagon's 2013 budget plan were announced Thursday, it was clear that some prominent remaining Cold War-era "systems" will live on.

That includes not just the B-52 bomber and the U-2 spy plane, but also the foundation of U.S. nuclear deterrence strategy: a "triad" of nuclear weapons that can be launched from land, sea, and air. That concept, credited by many for preventing nuclear conflict throughout the Cold War, is now seen by some arms control experts as the kind of outdated structure that the United States can afford to get rid of.

Some think the U.S. should do away with at least one leg of that "triad," perhaps the bomber role. That would not just save money and clear the way for larger reductions in the number of U.S. nuclear weapons _ an Obama goal in line with his April 2009 pledge to seek the elimination of nuclear weapons.

Carl Levin, D-Mich., chairman of the Senate Armed Services Committee, said recently that maintaining the current structure of American nuclear forces was "not in keeping with the modern world." He and like-minded lawmakers argue that nuclear weapons play no role in deterring threats such as global terrorists.

The U.S. now has about 5,000 operational nuclear weapons, about half as many as a decade ago. They can be launched from ballistic missile submarines, from underground silos housing intercontinental ballistic missiles, and from B-52 and B-2 bombers at air bases in Louisiana, North Dakota and Missouri.

The Air Force, which provides the land and air legs of the triad, argues for preserving that Cold War-era configuration.

"It remains our conviction that as you go down (in numbers of nuclear weapons), the triad actually becomes more important," Gen. Norton Schwartz, the Air Force chief of staff, told reporters Friday. "The diversity, the variety, the attributes associated with each leg of the triad reinforce each other to a greater degree."

Both the B-52 and the B-2 are capable of doing more than carrying nuclear weapons. The B-52 has been modernized many times and is now used in a variety of roles, including close-air support of troops in conflict and can carry missiles, bombs and mines. The first of the current H models entered service in May 1961.

The land-based intercontinental ballistic missile (ICBM) force dates to 1959. Ballistic missile subs, known as "boomers," were first launched in 1960; the current Ohio-class fleet dates to 1981.

The administration is nearing completion of an internal review of how many nuclear weapons are required to meet today's security needs; that process will lead to decisions on whether to reshape the nuclear arsenal. That effort is linked to consultations with NATO allies on whether to withdraw the remaining U.S. nuclear weapons from Europe, an arrangement that also is rooted in the Cold War. Also at play is how to set the stage for a new round of nuclear reduction talks with Russia.

The only move the Pentagon is making on the nuclear weapons front in the 2013 budget is a proposed two-year delay in development of a new generation of submarines to replace those how equipped with Trident nuclear missiles.

The Arms Control Association, which favors cutting nuclear weapons, estimates that the new fleet of ballistic missile submarines would cost $350 billion to build and would last for 50 years. It advocates shrinking the number of subs to eight, which is says would save $27 billion over 10 years.

Laicie Olson, senior policy analyst at the Center for Arms Control and Non-Proliferation, said in an interview Friday that she was surprised, given Obama's commitment to reducing the number of nuclear weapons, that the administration is not using its 2013 defense budget to take substantial steps in that direction.

"All of these things are sticking around," she said, referring also to the U-2 spy plane, which was to have been retired in 2015 and replaced by a high-tech successor, the Global Hawk, which is flown without a pilot aboard.

Preserving such Cold War-era weapons "actually seems like the opposite of what the president set out to do," she said.

The Pentagon announced Thursday that the Global Hawk turned out to be a disappointment and no cheaper to use, so it is being canceled. As a result, the Air Force is extending the lifespan of the U-2, nicknamed "Angel" by Kelly Johnson, the Lockheed engineer who helped design the high-altitude spy plane.

Since 1994 the Air Force has spent $1.7 billion to modernize the U-2, whose claims to fame include the October 1962 flights over Cuba that confirmed the presence of Soviet nuclear missiles, touching off the Cuban missile crisis.

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Online:

Pentagon: http://tinyurl.com/84ouz2u

Center for Arms Control and Non-Proliferation: http://armscontrolcenter.org/

Arms Control Association: http://www.armscontrol.org

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Robert Burns can be followed on Twitter at http://twitter.com/robertburnsAP