President Bush on Wednesday pledged $500 million to help fight the spread of AIDS in Africa and the Caribbean, a pandemic he said "staggers the imagination and shocks the conscience." The money would go to programs aimed at preventing mother-to-child transmission of the virus, which generally can be stopped with a regimen of drugs. Some 95 percent of the estimated 40 million HIV/AIDS sufferers live in developing countries, most of them in sub-Saharan Africa. Speaking in the White House Rose Garden, Bush said more funding could follow this initial effort, and urged other industrial nations and international organizations to follow suit.