The International Federation of Red Cross and Red Crescent Societies has launched an appeal to help victims of the devastating tidal waves that hit south and east Asia on December 26 - putting in place what looks
set to be its largest emergency relief operation ever. The disaster left at least 120,000 people dead, hundreds of thousands injured and millions displaced.
simply gives the writer a little more wiggle room if something goes wrong. From his limited perspective it appears 'set to be', but he doesn't know everything
for example, a boxer that looks set to be the next champ might actually have a serious injury that no one knows about
so what the writer is saying is 'they are organizing what appears, from my limited perspective, such a massive operation that it will probably be (barring unforseen circumstances) the largest such operation ever'