Q+A: Issues for future U.S./Russia arms deal

(Reuters) - Russian President Dmitry Medvedev and U.S. President Barack Obama said on Wednesday they will pursue an arms deal cutting nuclear warheads below levels agreed in 2002 in their first step toward mending relations.

Following are some of the key issues.

HOW WOULD THIS ADVANCE PREVIOUS DEALS?

The leaders said the proposed arms deal would go beyond the 2002 Strategic Offensive Reductions Treaty (SORT), which committed both sides to cutting arsenals to between 1,700 and 2,200 warheads by 2012.

It would replace the 1991 Strategic Arms Reduction Treaty (START I), which led to the largest bilateral reductions of nuclear weapons in history, and is due to expire in December.

HOW MANY WARHEADS DO BOTH SIDES HAVE NOW?

According to the Carnegie Endowment for International Peace, Russia currently has 3,113 strategic warheads compared with 3,575 for the United States. (www.carnegieendowment.org)

WHY DOES A NEW DEAL MATTER?

Russia sees START 1 as the cornerstone of post-Cold War arms control and believes that letting it lapse with no replacement could upset the strategic balance. Both sides see a new deal as a way to "press the reset button" on relations, which have been damaged by last year's Russia-Georgia war, differences over a planned U.S. missile shield in Eastern Europe and Moscow's opposition to NATO membership for Ukraine and Georgia.

WHAT ARE THE HARD ISSUES?

The negotiations will focus on how warheads are counted and how they can be deployed on delivery vehicles. For example, if a missile carries 10 independent warheads, does it count as a single weapon or 10? Russia insists on counting all warheads but the United States believes that only those deployed on existing missiles, not those that are in storage, should be counted.

WHAT ABOUT THE U.S. MISSILE SHIELD PLAN?

U.S. plans to develop a missile system in Europe may be drawn into the negotiations as Russia argues that it would also affect the strategic balance and weaken its position. Washington says the system is aimed at intercepting missiles from hostile states such as Iran, and is not directed against Moscow.

WHAT HAPPENS NEXT?

Negotiators are due to report back by July, when Obama will travel to Moscow for a summit. A U.S. official said "it's pretty clear that we have to hit some milestones" by then.