This week's summit between Russian President Boris Yeltsin and President Bush almost certainly will be the last major bilateral arms control meeting this century and possibly for decades.

After 15 years of painful, arduous negotiations, the nuclear arms agreement between Yeltsin and Bush astonished diplomats on both sides. Negotiators had worked only five months, and on the eve of the summit they weren't even sure they could work out their differences.But in a few hours the two leaders agreed to reduce long-range nuclear warheads by two-thirds of current levels to between 3,000 and 3,500 for each country by the year 2003 at the latest.

This means that further reductions would almost certainly have to be done through a global treaty because the new levels would bring the U.S. and Russian nuclear missiles much closer to the levels of other countries - Britain, France and China.

If the world ever decides to ban long-range missiles entirely, many countries would have to be involved. By then, the human race may have either learned the folly of weapons of mass destruction or have developed a new generation of weapon not even dreamed of now.

In front of an admiring joint session of Congress, which greeted him with thunderous applause and 11 standing ovations Wednesday, Yeltsin pledged that Russia's biggest missiles - the long-feared SS-18 long-range intercontinental ballistic missiles aimed at the United States - are already being taken off alert.

The West is puzzled why Yeltsin agreed to dismantle the SS-18 but agreed to let the United States keep about half of its submarine-launched multiple warhead missiles. His hardline opponents at home already are squawking.

Yeltsin said the arms race impoverished half his people and that his country couldn't afford it anymore. But he won't save much by getting rid of missiles already in place.

Some Bush administration officials speculated that until the agreement is implemented and the missiles destroyed, the West now has a huge stake in Yeltsin's political survival and Russian stability. Yeltsin said Wednesday there won't be a second chance if he fails.

The summit marked the end of arms control as a major issue, the end of the communist threat to peace and the formal armistice of the Cold War.

Yeltsin and Bush agreed that nuclear arms will remain but as a deterrent to terrorist countries and aggression and not as part of a race among superpowers for military superiority.

The next era, already begun, is about superiority of a different kind - economic competition.