ONE can understand the frustration and, perhaps, compassion fatigue that lay behind last week's agreement by Britain to return to Vietnam tens of thousands of "boat people" who are detained in Hong Kong. Still, it seems a peremptory way to solve a complex problem - sending legions of frightened and despairing people back to one of the most unreformed communist states left in the world.To be sure, Hong Kong is in a bind. More than 63,000 Vietnamese boat people are held in camps - prisons, really - and hundreds more arrive each week. Local authorities are increasingly worried about explosions of violence in the overcrowded camps. British and Hong Kong officials insist that the people who will be sent back to Vietnam against their will are not true refugees - people fleeing persecution and protected by international law - but are simply in search of better lives than those they left behind in impoverished Vietnam. For Hong Kong, with its limited territory and strained resources, to send these migrants back is no different, they say, from the US's forcing illegal immigrants to return to Mexico. However, distinguishing political refugees from economic ones isn't always easy. Hong Kong's screening process has shortcomings. And there is a difference between sending Mexicans back across the Rio Grande and forcibly returning boat people to a country that, at least until recently, had in place the full state-terror apparatus of a Leninist regime. The US rightly has opposed all involuntary repatriation of people who have fled Vietnam. No doubt it's true that a large portion of the boat people are economic migrants, especially among more recent arrivals. Even so, there is merit in delaying the return of these people awhile longer, as the world community assesses changes going on in Vietnam and bolsters procedures for monitoring the safety of returning migrants. Vietnam is eager to end its diplomatic isolation and to have the US economic embargo lifted. These were factors in its agreement to the Cambodian peace pact, and they are contributing to political and economic reforms inside the country. Hanoi has pledged not to persecute returning boat people and to permit the United Nations High Commissioner for Refugees to monitor the conditions of returnees. These are encouraging developments. Together with improved economic conditions as more international trade and investment start to flow to Vietnam, they should produce a climate in which many of those who fled Vietnam will choose to go home. But the process of change is not complete. With a bit more patience, Britain and Hong Kong should be able to end their refugee crisis in a way that reflects credit on their human rights values, rather than in a way that appears to compromise them.