The annals of PR are rife with tasteless attempts to score points off bad news. A post-9/11 bid to soothe a traumatized nation with the healing power of Hot Pockets comes to mind.But last week, a handful of senators - hardly America's greatest arbiters of tact - managed to reignite a national debate about stem-cell research during a frenzied wave of global mourning. And they did it without rousing a single cry of exploitation or opportunism. Granted, a certain morbid serendipity was on their side. Fifty-eight senators, Democrat and Republican alike, sent a letter to the White House asking President Bush to make additional lines of stem cells available for research less than 24 hours before former President Reagan died after a 10-year bout with Alzheimer's - one of the diseases proponents claim such research may help cure. But it took a rare blend of subtlety and chutzpah to make that letter public on Monday morning, not to mention feed respectful quotes to the media throughout the week that would push the issue without pushing the envelope. By all measures, they pulled it off. Not only did the story make the perfect complement to the otherwise all-Reagan, all-the-time news scene last week, it struck enough of a chord publicly to force the White House and even the First Lady to repeatedly defend what was at least temporarily the unpopular side of the issue. Breaking through a media blackout spurred by national tragedy - without appearing exploitative - is one of the most delicate challenges a PR person can face. In a week of occasionally over-the-top tributes to The Great Communicator, the senators' achievement may have been the most fitting.