Chief elements of the U.S.-Russia nuclear arms treaty called New START:

NEW LIMITS ON STRATEGIC NUCLEAR WEAPONS: Each side would have to limit their arsenal of warheads ready to launch to 1550. That's down nearly 30 per cent from the limits imposed in the last U.S-Russia nuclear pact, the 2002 Moscow treaty.

NEW LIMITS ON MISSILE DELIVERY SYSTEMS: The treaty also limits missiles, bombers and launchers capable of carrying nuclear warheads. Each side will be allowed up to 800 submarine launched ballistic missiles, heavy bombers and intercontinental ballistic missiles, whether they are deployed or not. Of all of these only 700 can be nuclear armed. This halves the limits under the 1991 START treaty.

VERIFICATION: The treaty restores elements of the system under the previous START treaty that allowed each side to verify that the other was sticking to treaty terms. The old system expired with the START treaty just over a year ago and neither side has had inspectors on the ground monitoring the other's arsenals since then. The new treaty would include key changes that the Obama administration says would make inspections cheaper and easier. It would add, for instance a numbered inventory of items relevant to the limits in the two arsenals. Each missile and heavy bomber will have unique data identifying it. The treaty would allow 10 short notice inspections of ICBM, submarine and air bases annually and an additional eight inspections of storage facilities for non-deployed warheads.

WHAT THE TREATY DOESN'T DO: The treaty does not limit warheads that are in storage and not ready to launch, though it does allow monitoring of those assets. It also does not limit nuclear warheads intended for short range delivery to counter conventional armies. These smaller warheads are known as tactical nuclear weapons. The Obama administration has said it would like to negotiate with Russia new limits on both non-deployed warheads and tactical weapons in a follow-up treaty after New START is ratified. The treaty also does not impose any significant limitations on the countries' ability to build missile defense systems, as critics have charged.