B757-200 CREW WAS SPACED TOO CLOSED TO A PRECEDING B757 AT LAS. CREW WAS TOLD TO 'DO WHATEVER YOU NEED TO DO' TO PROVIDE SPACING. JUST AFTER PASSING THE RWY THRESHOLD THEY HIT THE WAKE OF THE OTHER B757.

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LAS GAR. WE WERE ASSIGNED THE LYNSY.LYNSY1 ARR. AFTER PASSING PGS; WE WERE CLRED DIRECT UTARE. ARRIVING AT UTARE; WE WERE ADVISED BY APCH THAT WE WERE NOW WAY TOO CLOSE TO A PRECEDING B757 AND DO WHAT YOU HAVE TO TO ENSURE SEPARATION. ATC APPARENTLY KEPT THE PRECEDING B757 UP TOO HIGH; TOO CLOSE; AND NOW THEY DID THE SAME TO US. HERE WE ARE -- 2 B757'S S-TURNING LIKE CRAZY; TRYING TO GET DOWN -- AND IN OUR CASE; TO GET DOWN AND ALSO GET AT LEAST A MINIMUM OF 5 MI OF SEPARATION ON THE PRECEDING B757. AT ONE POINT WE WERE SLOWED DOWN TO 170 KTS IN THE VICINITY OF 5000 FT ALT. I MANAGED TO GET THE SEPARATION AND GET DOWN TO THE GS. WE WERE CLRED TO A 'VISUAL APCH TO RWY 25L; MAINTAIN VISUAL SEPARATION WITH PRECEDING ACFT.' THE WIND AT THIS POINT WAS ABOUT 230 DEGS AT 15 KTS GUSTING TO 27 KTS. WE HAD A HEALTHY L CRAB GOING ALL THE WAY DOWN TO AROUND 60 FT RA. ALMOST SIMULTANEOUSLY WITH ME INITIATING A FORWARD SLIP FOR RWY ALIGNMENT; WE HIT I BELIEVE THE WAKE OF THE PRECEDING ACFT. WE ROLLED SHARPLY TO THE L. IT FELT LIKE 15-20 DEGS FOLLOWED IMMEDIATELY BY A SHARP SAME AMOUNT OF DEG ROLL TO THE R. THIS HAPPENED SO FAST THAT BY THE TIME I HAD INITIATED A FIREWALL THRUST IMMEDIATELY FLEW OUT OF HIS WAKE; BUT GOT A ROUGH RIDE ALL THE WAY AROUND FOR ANOTHER APCH; AND AT THIS TIME; A NICE LNDG. I CAN ONLY GUESS THE AMOUNT OF FT OUR WINGTIPS MISSED THE TERRAIN.