President Barack Obama has told the bosses of 13 US credit card issuers to ditch unfair interest rate hikes and to be more transparent and accountable.   Obama wanted to keep the credit card market but to "eliminate some of the abuses" as politicians have expressed anger that many of the banks issuing credit cards with high fees are the same banks that have received government bailout money.   Banks say tighter rules would reduce income at a difficult time for them.