Nuts and bolts of Start 2 agreement: The new strategic arms reduction treaty signed yesterday by Presidents Bush and Yeltsin for the United States and Russia contains six main points

The total number of nuclear warheads on each side is to be set at between 3,800 and 4,250 for the first seven years after the treaty comes into force.

As from 1 January 2003, the figure is to drop to between 3,000 and 3,500, marking a two- thirds reduction of the two countries' current strategic nuclear arsenals.

The number of submarine-based missiles within 10 years cannot exceed 1,750.

That will require America to dismantle about half of its 432 Trident I and II missiles, which have eight warheads apiece and which formed the chief component of the US deterrent.

By 1 January 2003 land-based intercontinental ballistic missiles with multiple and independently targeted warheads (MIRVs) will all have been removed, either through straightforward elimination or through conversion, up to a maximum of 90, to a single warhead by adapting the launching pads.

This point meets an important Russian claim concerning the transformation of 90 launch pads for SS-18 missiles to take SS-25s. Under the first Start treaty, signed in July 1991 by George Bush and the then Soviet leader, Mikhail Gorbachev, Russia is already committed to dismantling half of its 308 SS-18 missiles. The SS-18 missiles can carry up to 10 nuclear warheads.

Each country has the right to change 105 land-based multiple-warhead missiles into single-warhead missiles by removing a maximum of five warheads. That meets another Russian claim, as Moscow, for reasons of economy, wants to convert 105 of its 170 SS-19 missiles with six warheads into single-warhead weapons.

For nuclear bombers, the number of warheads per plane type is to be specified in a memorandum attached to the treaty. Lists will be presented for inspection by the other side in the 180 days after the treaty takes effect. Up to 100 nuclear bombers may be reconverted to conventional use by each country.

The text makes it clear the new treaty cannot take effect before the provisions of Start 1 have been applied. Ukraine has yet to ratify the Start 1 treaty.

An appendix attached to the treaty spells out precisely how launch pads are to be converted to take single-warhead weapons. A

5-metre (16.5ft) layer of concrete is to be poured into the base, and a restrictive ring with a diameter of no more than 2.9 metres (9.5ft) is to be attached to the upper part.

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