When Diana Spencer has been laid to rest; when the Windsors have resumed tending their moribund estate; when the clamor over paparazzi and Dodi Fayed and drunk driving has subsided; after all that, the world can honor the memory of the Princess of Wales by attending to the message she delivered in the final months of her life."Having seen for myself the devastation that anti-personnel land mines cause," she told a Washington, D.C., audience last June, "I am committed to supporting in whatever way I can the international campaign to outlaw these dreadful weapons."Diana did more than raise her deceptively soft voice against a mechanical scourge that takes the lives of children every day. She presumed to act, with bold disregard for the conventions of her position and the sneering of her intellectual superiors. And there is no question that in her dewy-eyed, style-setting, camera-ready way, she pushed the nations of the earth toward the prospect of a ban on land mines that only a few years ago seemed impossible.She apparently was surprised by the nasty reaction last January when she joined the Red CrossÕ international campaign against land mines during a trip to Angola, the second-most heavily mined place in the world. She didn't seem to realize that back in London and New York, it would be easy to sound clever at cocktail parties by smirking about her new commitment. Quite predictably, she was mocked as a dim, flighty female who had no business meddling in (male) matters of state.Of course, it was not Diana but her glib detractors who were truly dim. Few of them understood the political, emotional and even physical risks she courted by entering the land-mine debate. Nor, because their own lives are so narrowly self-centered, could such people grasp the profound gratitude felt by those she aided, the wounded nobodies whom she raised above the media's mindless din.But if the smart sorts didn't take Diana seriously, the politicians were too smart not to. She was savaged anonymously by Tory leaders who called her "a loose cannon," "a birdbrain" and worse, because they feared her ability to mobilize opinion against the profitable trade in indiscriminate death. When those assaults backfired, the Tory Government tried to neutralize the Princess by claiming that it shared her objectives.Diana ignored this lie, knowing that while Her Majesty's Government gave lip service to a "universal ban on land mines," it lobbied the United Nations to exempt British mines from the weak restrictions being contemplated endlessly in Geneva. She knew, as she told Le Monde in a recent interview, that on the subject of land mines, the Tories, unlike Labor, were simply "hopeless." Until lately, the United States was guilty of a similar hypocrisy, although President Bill Clinton was among the first heads of state to proclaim his support for a land-mine ban. When the Canadians began to lobby for an international treaty, the President spurned their plan in favor of a U.N. negotiating process that was foredoomed to failure. He finally bucked the Pentagon's relentless pressure a few weeks ago, when he reversed position to join Canada (albeit with reservations about de-mining the Korean peninsula). No doubt Mr. Clinton's turnabout was due to the popular momentum Diana helped create by the force of her personality--a momentum that finally may prove unstoppable.Such an outcome seemed beyond hope back in 1993, when an excellent book-length report on the worldwide plague of land mines was jointly published by the Arms Project of Human Rights Watch and Physicians for Human Rights. Detailing the enormous problems posed by an estimated 110 million mines strewn beneath the fields and roads of some 62 countries--with millions more being deployed annually--the report's authors conceded that their advocacy of a total ban on production, stockpiling and sales of land mines "may be viewed as quixotic." Now it is a realistic goal that may be achieved as soon as December. That's when the Canadians hope to host the great majority of the world's nations at the signing of a treaty banning land mines, though Russia, China, Israel and a number of others still are refusing to participate. Ottawa's diplomats and nongovernmental groups such as the Red Cross certainly will deserve most of the credit--yet they all acknowledge that the Princess played a critical role."I don't want to overestimate Diana's contribution," a top Canadian arms control official told The Toronto Star, "but she brought a level of media hype and public attention to the issue that never existed before, and it brought pressure on governments." Not bad for a na•ve clotheshorse who decided that the killing and maiming of thousands was too appalling to continue. Diana was sensitive enough to be hurt by the relentless scorn and ridicule, but strong enough to persevere. She should have lived to see the end of the random carnage she opposed with such admirable courage and grace. In her own senseless death, we have learned that it is possible to despise monarchy, aristocracy and everything these institutions represent, and somehow to mourn all the more deeply the passing of the People's Princess.