The high-level meetings ahead between the US and Russia are likely to be followed by intense activity as the two sides strive to map out a fresh accord by the Dec. 5 deadline.
Often described as the most effective arms control accord in history, START led to the removal of more than two-thirds of all strategic weapons and limited each side to the then-radical ceiling of 6,000 warheads deployed on no more than 1,600 delivery systems.
Moscow welcomes Obama's goal
But experts warn that the global security environment has shifted dangerously in two decades, and the old bipolar superpower standoff has been deeply complicated by the emergence of new nuclear wild cards, such as India, Pakistan, and North Korea.
They also worry that the old arms control framework may have been fatally damaged by the Bush administration's unilateral withdrawal from the 1972 Anti-Ballistic Missile Treaty, which banned defensive strategic weapons, followed by a decision to station anti-missile interceptors in Poland. Despite such concerns, official Moscow appears enthusiastic.