A dam upstream of the towns of Quebradillas and Isabela in northwest Puerto Rico was cracked but had not burst by Saturday night as water continued to pour out of rain-swollen Lake Guajataca. Federal officials said Friday that 70,000 people, the number who live in the surrounding area, would have to be evacuated. But Javier Jimenez, mayor of the nearby town of San Sebastian, said he believed the number was far smaller.