BOMB or talk? As the recent debate over use of the A-bomb to hasten Japan's World War II surrender reminds us, one of history's perennial anguished questions is whether massive force or persuasive talk works better to end wars. It may sound simplistic to answer that both are usually necessary. But studies of the diverse wars cluttering history books support that conclusion. The question is relevant once more because the muddled, savage, media-conscious Bosnian war has reached the point where peace talk is furthered by the kind of decisive reaction UN/NATO forces have just taken. That's the NATO air and artillery attacks against Serbian positions that have bombarded Sarajevo with murderous irregularity. When Serb mortars hit the Bosnian capital one time too many after a clear UN/NATO warning, the response was what one commentator called a sledgehammer after months of using tweezers. Serb tacticians have been masters at playing Western leaders' patience just to the limit but not over. We'll now see whether they want to continue playing the tactic of bite, digest, retreat; or whether they have been sobered into seriously bargaining over the US-proposed peace settlement. The problem facing the US plan for settling boundaries and buffering them with UN forces is that all three territory-seekers need to be corralled at the same time. That means the Bosnian Serbs must calculate that they have more to lose than gain by prolonging the conflict. The Bosnian Muslims must realize that NATO's muscle-flex was limited to defending their capital as a UN-declared safe area. It's not a license to expect NATO support for an offensive. And Croatia's Franjo Tudjman must not be led to assume he will get further winks from Washington if he attempts to swallow more territory. A tall order. But NATO's sudden decisiveness just may be the beginning of making it work. The key litmus indicator is likely to be Bosnia's Serbs. Will their leaders get serious about a final peace/borders deal? Or will they simply toy with the US proposal and then take another bite out of the remaining safe havens to test Western resolve? Much depends on whether that resolve is unmistakably clear. Peace in the savage Bosnian war is aided by NATO's decisive action.