Bolivia's Knot: No to Cocaine, but Yes to Coca
Newly elected Bolivian Pres Evo Morales has not yet provided many details of his coca policy, except to say that his government will depenalize cocoa cultivation and show zero tolerance to cocaine trafficking; has long opposed American eradication efforts and championed coca leaf; must find ways to reassure foreign governments and investors that Bolivia will control trafficking; United States fears that progress toward eradication in Colombia could be offset by burst of cultivation in Bolivia; photos; map (L)