THE conclusion of another nuclear-arms reduction pact between the United States and Russia is a propitious way to begin 1993, even though the full benefits of the agreement may not be evident until 2003. The Start II treaty - the second phase of the Strategic Arms Reduction Talks - could steer the world sharply away from the threat of nuclear warfare.
"Could" is the operative word, since the signing of the treaty by Presidents Yeltsin and Bush only initiates a process that has a difficult political prelude before it ever gets down to dismantling missile silos.
An important part of that political phase is tied to an earlier agreement, Start I, signed in July 1991. That treaty has to be implemented ahead of Start II, but it has yet to be ratified by Russia's neighboring nuclear republics - Ukraine, Kazakhstan, and Belarus. The latter two are likely to approve the pact without major hitches. But Ukraine's government has made clear its desire to get paid for the highly enriched uranium in the warheads and to get strong security assurances from both the West and Ru ssia.
Those concerns, however, have to be weighed against Ukraine's interest in cementing good relations with the West. That interest dictates its ratification of Start I.
An equally difficult time awaits Start II in the Russian parliament. Hard-liners remain suspicious of American motives. They will decry sharp cuts in Russia's top-line land-based missiles while the US retains much of its prized submarine-based nuclear force.
But the US did its share of compromising to make Start II possible: Russia will retain 90 silos that house its SS-18s, and it will be able to inspect American nuclear-armed bombers.
Most important are the central goals of the pact - elimination of destabilizing land-based missiles with multiple warheads and a two-thirds reduction in the number of warheads overall.
Those goals are distant promises, as yet. But once inspectors and technicians start blowing up silos, things can move quickly. The warheads themselves won't be destroyed, though the dangers they pose are greatly reduced by the elimination of launching systems. The hard slogging of START I and II will fully pay off only if the whole world is steered toward nuclear disarmament, which means a much-strengthened nuclear nonproliferation treaty.
The prospects of that will be greatly enhanced if the US and Russia set a good example in implementing START Iand II - and if the Ukraine, Kazakhstan, and Belarus exhibit the good sense to get rid of the nukes on their territory.