To evaluate the relative effectiveness and safety of foscarnet versus ganciclovir for the treatment of cytomegalovirus (CMV) retinitis in people with AIDS; to evaluate the relative effect on survival of the use of these two anti-CMV agents in the treatment of CMV retinitis; to compare the relative benefits of immediate treatment with foscarnet or ganciclovir versus deferral of treatment for CMV retinitis limited to less than 25 percent of zones 2 and 3.