Maybe it was the influence of his wife, Laura, a former librarian, or his mother, Barbara, a longtime promoter of literacy. Or perhaps he was just eager to dispel his image as an intellectual lightweight. But President Bush now wants it known that he is a man of letters. In fact, Bush has entered a book-reading competition with Karl Rove, his political adviser. White House aides say the president has read 60 books so far this year (while the brainy Rove, to Bush’s competitive delight, has racked up only 50).