Q+A: Key issues under debate on new START treaty

WASHINGTON (Reuters) - The new START nuclear arms treaty under debate in the U.S. Senate is generating criticism among Republicans, including potential 2012 presidential contender Mitt Romney, who says it may be President Barack Obama's "worst foreign policy mistake yet."

Following are questions and answers that have been raised about the treaty:

WILL THE TREATY IMPEDE U.S. EFFORTS TO BUILD AN ANTI-MISSILE DEFENSE SYSTEM?

Romney, the former Massachusetts governor, and some Republican lawmakers say the treaty may hamper U.S. missile defense efforts. The accord makes few references to missile defense. In the preamble it says the two sides recognize a relationship between strategic offensive and defensive weapons. Romney and some other Republicans argue the preamble language is a victory for the Russians, who have been using it to assert that the treaty places a limit on U.S. missile defenses.

Treaty proponents say the accord does not put specific limits on missile defense systems. They say the remarks in the preamble only state the obvious: The point of the treaty is to maintain a strategic balance and give both sides the confidence to reduce the size of their nuclear arsenals. If one side aggressively builds up its defensive anti-missile capability, it would destroy the balance by rendering the other side's reduced nuclear offense ineffective.

DOESN'T THE TREATY LIMIT U.S. MISSILE DEFENSE BY FORBIDDING THE CONVERSION OF INTERCONTINENTAL BALLISTIC MISSILE SILOS INTO MISSILE DEFENSE SILOS?

Romney, former Senator Jim Talent and experts at the conservative Heritage Foundation think tank say this restriction would hamper U.S. efforts to build an anti-missile defense system.

Treaty proponents say the provision does not affect the U.S. anti-missile defense effort because the United States has no plans to try to convert the silos for defensive purposes.

Steven Pifer, director of the Arms Control Initiative at the Brookings Institution think tank, said U.S. officials have testified to Congress that it costs about $20 million more convert a silo than to build a new one.

Mort Halperin, who served on a panel that reviewed U.S. strategic posture for Congress, said it would be unwise to base defensive missiles in a location where their firing could be misconstrued by Russia as an attack.

"The last thing you want to do in a tense crisis is to fire 50 objects up from the missile field in a way that the Russians would have to feel was coming at them and might lead them to fire in retaliation," he told a briefing at Brookings.

HAS RUSSIA WEAKENED THE TREATY BY RESERVING THE RIGHT TO WALK AWAY FROM IT IF THE U.S. SIGNIFICANTLY ENHANCES ITS MISSILE DEFENSE?

Some treaty opponents say the accord undermines U.S. strategic defense because Russia has the right to withdraw from the new START agreement if the United States significantly enhances its missile defense.

Treaty advocates point out that either side has the right to withdraw from the treaty after giving three months notice. Republican Senator Richard Lugar, in a response to Romney, said, "Nothing in the treaty changes the bottom line that we control our own missile defense destiny, not Russia."

DOES THE TREATY GIVE RUSSIA AN ADVANTAGE BY NOT MENTIONING RAIL-BASED BALLISTIC MISSILES, WHICH MOSCOW HAS FIELDED IN THE PAST?

Some opponents argue the treaty has loopholes that would enable Moscow to avoid the accord's limits on launchers or missiles, for example by mounting them on railroad cars as they have in the past.

Treaty proponents say Russia deactivated its last rail-based missiles in 2008. While the treaty doesn't expressly mention missiles on rail cars, proponents say such missiles would be covered by the broad definitions of warheads and launchers included in the treaty.

THE TREATY ONLY COUNTS BOMBERS AS ONE WEAPON, EVEN THOUGH THEY CAN DELIVER SEVERAL BOMBS AT A TIME. DOES THIS GIVE RUSSIA AN UNFAIR ADVANTAGE?

Romney and some Republican lawmakers have raised this issue. They say Russia has discussed building a new heavy bomber and could circumvent the limits on nuclear arms by loading such aircraft with multiple weapons.

Proponents of the treaty say the practice of counting a bomber as one weapon, even though it could carry several nuclear bombs, dates back to Republican President Ronald Reagan, who originally suggested bombers not count at all.

They say bombers often perform nonnuclear duties, generally don't carry atomic bombs and fly much more slowly than missiles so it makes sense to treat them differently.

Treaty proponents also note that the bomber provision actually currently favors the United States, which has an estimated 113 heavy bombers to Russia's estimated 76.

IS THE UNITED STATES GIVING AWAY SOMETHING FOR NOTHING BY AGREEING TO THE TREATY'S CUTS IN MISSILE LAUNCHERS?

Treaty critics argue that the United States will have to eliminate some of its launchers in order to achieve the target of 800, while Russia already is below that number, will not have to eliminate many and could build more.

Treaty proponents counter that Russia has more nuclear warheads than the United States and will have to eliminate more warheads under the accord.

DOES THE START TREATY LEAVE RUSSIA WITH A MASSIVE ADVANTAGE IN TACTICAL NUCLEAR WEAPONS?

Senator John McCain, Romney and others say the treaty is flawed because it leaves Russia with a huge advantage in tactical nuclear weapons over the United States. Those weapons threaten U.S. allies in Europe, which depend upon a U.S. nuclear umbrella for protection, he and other treaty skeptics say.

Treaty proponents say START doesn't deal with shorter-range tactical nuclear arms because it is a strategic treaty that addresses long-range weapons. They say Russia maintains the tactical weapons to counter what it views as stronger U.S. conventional forces in Europe. They say the issue of tactical nuclear weapons should be addressed, but in a different treaty. They say they hope the completion of START will encourage the Russians to move ahead to negotiations on tactical nuclear arms.

(Reporting by David Alexander; Editing by Eric Walsh)