House and Senate Face Big Job To Settle Medicare Differences
House passes Medicare reform bill, 216 to 215, that would help elderly buy prescription drugs and Senate, in 76 to 21 vote, passes another version; congressional leaders rejoice over passage, but say it may take weeks, perhaps months, to iron out compromise complicated by extremely close House vote; Pres Bush praises action on one of his top domestic priorities; provisions of two bills compared; photo (M)