WASHINGTON — Washington. -- After a frustrating week, first dealing with Congress on the balanced-budget amendment and then dodging tear gas and brickbats in Latin America, President Bush scored a brilliant success during Russian President Boris Yeltsin's visit to Washington. After only five months of negotiation, and in two pages of sparse strategic jargon, the two presidents agreed to make the most sweeping reductions of nuclear weapons in history.
How significant was this deal? Just two years ago, the U.S. had 13,000 nuclear warheads in its strategic inventory and the Soviet Union had 11,000. One year ago, with the START treaty, the two nations agreed to cut these arsenals to about 7,000-8,000 over seven years. This week, the U.S. and the Soviet Union's main successor, Russia, agreed that within that same seven-year period they would reduce their strategic nuclear forces to between 3,800 and 4,250 warheads, ''as each nation shall determine.''
This means that if present political trends continue and the commitments undertaken last are implemented, strategic nuclear weapons in the hands of the two major nuclear powers will decrease by an astounding 70 percent in the last decade of this century.
Not only will the overall arsenals shrink, but the remaining forces will be much more stable and secure. The most destabilizing weapons -- land-based missiles with multiple warheads (MIRVs), the systems most likely to be launched first or pre-emptively attacked in a crisis -- will be banned on both sides. This means an increased proportion of U.S. and Russian deterrent forces will be based either at sea, where they are secure and survivable, or on aircraft, which take much more time than missiles to reach their targets and are recallable.
These massive, overall reductions, and Moscow's willingness to abandon its key MIRVed systems, would not have been possible without an accompanying, fundamental change in the way the Russians view their strategic relationship with the United States. Pledging that ''we shall not fight against each other,'' President Yeltsin, speaking from the White House Rose Garden, noted that Russia now needs only to maintain a ''minimum-security level'' of forces. With this agreement, he continued, the two nations were ''departing from [the concept of] parity, where each country was exerting every effort to stay in line, [and] which has led Russia, for instance, to have half its population living below the poverty line.''
Reflecting these changes in policy, the Russians sought the lowest overall limits on nuclear weapons -- they originally proposed 2,000 to 2,500 warheads, and the final language actually calls for between 3,000 and 3,500 ''or such lower numbers as each nation shall decide.'' In Washington, Mr. Yeltsin informed U.S. officials that Russia, for its part, intends to deploy its forces on the lower side of the permitted range.
After these breathtaking developments, what next? Clearly, an overriding policy goal for the U.S. -- and the West -- remains to ensure as best we can that the democratizing trends in Russia which brought about this stunning agreement are fostered and strengthened and that the forces behind last August's failed coup attempt do not finally succeed. Simply put, Mr. Yeltsin's willingness to support U.S. goals in the security arena should exact the price of U.S. economic and political support for Russian reforms and Russian reformers.
In addition, since this latest accord is related to, and dependent upon, the START treaty's entry into force, the Senate needs to move rapidly to ratify that earlier arms-reduction agreement. This may be more difficult than it seems for two reasons.
First, although the ratification hearings begin this week, the Senate must act swiftly because its calendar is shortened this year by recesses for the party conventions and the general elections.
Second, entry into force of START involves nudging along the three non-Russian republics with nuclear weapons on their territory -- Ukraine, Kazakhstan and Belarus. At best, these nations are ambivalent about giving up the nuclear weapons based in their countries; they could easily delay their own ratification processes. Moreover, after an elaborate series of state visits to the U.S. prior to being made parties to the START treaty last May in Lisbon, they may well bristle at being cut out of this most recent round of negotiations.
Finally, the reductions under this new accord will take until at least the end of the century, if not longer. A lot can happen in eight years, and the U.S. may well find it advantageous to intervene economically to accelerate the process. According to the Washington joint understanding, the timetable for removals can be compressed ''if the U.S. can contribute to the financing of the destruction or elimination of strategic offensive arms in Russia.'' That, together with the Louisiana Purchase and Seward's Folly, is bound to be one of the best national investments we will ever make.
Jack Mendelsohn, a retired foreign-service officer, is deputy director of the Arms Control Association.