START II PACT BUILDS ON TWO DECADES OF ARMS CONTROL

* The START II treaty signed yesterday will slash strategic nuclear weapons by more than two-thirds.

It brings Russia's arsenal back to where it stood in the 1970s and returns the United States arsenal to 1960s levels.

The two military superpowers now have roughly 21,000 atomic warheads between them. The new Strategic Arms Reduction Treaty (START) accord obliges both sides to reduce strategic arsenals to 3,000 to 3,500 warheads by Jan. 1, 2003, at the latest.

All land-based systems with multiple warheads - including the 10-warhead Russian SS-18 missile - are to be eliminated.

START II builds on a long history of arms accords and arms summits between Moscow and Washington, including several other major pacts signed during President Bush's tenure:

* July 30-31, 1991 - Mr. Bush and then-Soviet President Mikhail Gorbachev met in Moscow and signed the first Strategic Arms Reduction Treaty (START I) reducing stockpiles of long-range nuclear weapons by as much as 30 percent.

* Nov. 19, 1990 - Bush and Gorbachev met in Paris for a diplomatic summit to sign with European leaders the Conventional Forces in Europe treaty, making historic cuts in East-West conventional forces.

* December 1987 - Presidents Reagan and Gorbachev met in Washington and signed a treaty to destroy intermediate-range nuclear forces.

* June 1979 - President Carter and Soviet leader Leonid Brezhnev met in Vienna and signed the second Strategic Arms Limitation Treaty (SALT II) limiting nuclear missiles, bombers and cruise missiles. The treaty was never ratified by the US Senate but was observed informally by both sides until late 1986.

* June-July 1974 - In Moscow a month before President Nixon resigned under threat of impeachment in the Watergate scandal, he and Mr. Brezhnev signed accords limiting the yield of underground nuclear tests.

* May 1972 - Nixon and Brezhnev open era of "detente" during first Moscow visit by an incumbent US president. They signed SALT I, the first pact limiting US and Soviet nuclear arsenals, and the Antiballistic Missile Treaty, which limited each side's deployment of defensive systems.