William Clay Ford Jr., the 44-year-old great-grandson of founder Henry Ford and already chairman of the world's second-largest automaker, replaced embattled President and Chief Executive Jacques Nasser yesterday...As chairman, Ford's most visible efforts have been moves to make the automaker more environmentally friendly, such as the company's pledge to raise the fuel economy of its sport utility vehicles by 25 percent by 2005. Ford has struggled to unite the drive for greater profits with social responsibility, arguing consumers would reward companies which thought about more than simply profit and loss. In the past few years, Ford has reached out to environmental groups such as Greenpeace and admitted the polluting nature of some of its vehicles - something unheard of in Detroit.