Washington had better exert more pressure on Moscow to keep withdrawing Russian troops from Afghanistan.

If that isn't done, the Soviet pledge to complete the pullout by next Feb. 15 could easily fall apart just when it looked like an end to the bloodshed might finally be in sight.The need for continued pressure on Moscow should be clear from recent reports that the Soviet Union has not only slowed the pace of its withdrawal, but also become more actively involved in fighting Afghan rebels.

Just how much the situation has worsened can be seen from a few key facts. In the two months that ended July 15, the Soviets had withdrawn only 20,000 to 30,000 troops, or about one-quarter of the force they had deployed in Afghanistan. To fulfill the commitment Russia made to remove half its troops by mid-August, Moscow must withdraw another 20,000 to 30,000 troops in little more than three weeks.

Put another way, two-thirds of the way into the first major phase of the withdrawal, the Soviets have withdrawn only about half the force they are committed to remove by Aug. 15.

As the Soviets leave, the Afghan rebels grow bolder and more successful. Recently they destroyed eight Soviet ground-attack planes at the Kabul airport. Rebels also have overrun an Afghan communist stronghold at Ali Khel in the eastern part of the country, capturing more munitions in one stroke than the entire resistance gets from the CIA in three months.

Though such rebel successes must gall the Soviets and terrify their puppet regime in Kabul, Moscow should have known that any military withdrawal becomes more difficult the further it goes. Moscow also should be told that such difficulties won't be accepted as an excuse for reneging on the withdrawal agreement made last April in Geneva.

The world needs to keep watching the situation in Afghanistan carefully and keep demanding that the Soviets honor their promises to go home.