GEORGE BUSH has reviewed the assessments given him by the State Department and decided that the time has come to lift economic sanctions against South Africa. Since the president had doubts about sanctions from the beginning, this was, perhaps, not a terribly difficult conclusion for him to arrive at.From the White House's point of view, the matter is cut and dried. The five conditions set by the 1986 law establishing sanctions have been met. But that, of course, is hotly debated by those who feel the economic embargo remains a vital tool to force democratic change in South Africa. Have all political prisoners really been released? That's a question of definition, and while hundreds certainly have been freed, others remain behind bars - as criminals locked up for deeds of violence, Pretoria would argue. Has the South African government really begun the "good faith" negotiations called for by US law? There have been talks, but it's debatable whether they yet constitute solid negotiations. President De Klerk now promises rapid progress toward substantive talks with the African National Congress (ANC) and other parties, leading to the drafting of a new constitution for the country within the next year. It's critical to the health of those talks that the violence that has beset South Africa's black communities for much of the past year be stopped. The government's swift efforts to stop factional bloodsh ed would be a critical indication of its "good faith." Now that the US has moved to dismantle sanctions, it has to be hoped that all sides in South Africa will take this as an incentive to plunge wholeheartedly into negotiations. The ANC, because it recognizes that the Bush administration's action, plus the International Olympic Committee's decision to bring South Africa back into the sports fold, virtually brings down the curtain on sanctions as a lever it can use to force concessions from Pretoria in anticipation of talks. And the government, because it's now seeing tangible rewards from its demolition of apartheid's legal structure and will want to see even more. Not all sanctions will fall at once, either. In the US, state and local restrictions on doing business with South Africa remain, as do some federal bars to international financial assistance. The pressure is not off entirely, and in fact must not be. The US government should remain vigilant to do all it can to press reforms forward, so that the still far-from-attained goal - a South Africa where all citizens have the vote and a clear say in how their country is run - can most quickly be reached.