BUT IN POLITICAL MINEFIELD, REAL PLAN ISN'T FEASIBLE, ANALYSTS SAY NEW YORK TIMES NEWS SERVICE WASHINGTON - President Bush's vision of an "ownership society" is built more than anything else on a sweeping promise: that he will transform Social Security so younger workers can divert some of their payroll taxes into private investment accounts. At a rally in Pennsylvania last week, Bush declared, as he does at almost every campaign stop nowadays, that "younger workers ought to be able to take some of their taxes and set up a personal savings account, an account that they can call their own,...