(FORTUNE Magazine) – The five-year-old drive to extend global trading rules to new areas, such as services and agriculture, is in trouble. Seeking arresting arguments, GATT Director General Arthur Dunkel in May hired Columbia University economist Jagdish Bhagwati, 56, as his personal adviser. Says Dunkel: ''He combines solid analysis with sensitivity to political debate.'' An arch free-trader, Bhagwati is also independent-minded enough to break ranks with his ideological kin on a U.S-Mexico free-trade agreement. Says he: ''I don't see great goodies for us in immigration or trade.'' The economist's larger concern is that a Mexico deal could sidetrack GATT talks by leading the U.S. down a regionalist road at a time when multilateralism is crucial. ''What signal does it send?'' he asks. ''Asians have already seen 1992 absorb Europe's attention.'' Does he worry that straight talk might ruffle feathers at GATT's Geneva headquarters? Hardly. Says the Indian-born author of 17 books: ''If professors don't take unpopular positions, who the hell will?''