B7676-300 CREW HAD AN EICAS WARNING 'LEADING EDGE SLAT DISAGREE' GOING INTO SAN.

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AFTER PASSING EDSEL AT FL350 AND MACH .810; THE LEADING EDGE LIGHT; LEADING EDGE SLAT; DISAGREE EICAS AND THE CAUTION LIGHT ALL CAME ON. THE QRH ADVISES THAT IN THIS CASE WE WOULD BE LIMITED TO FLAPS 20 DEGS FOR LNDG. WE GOT A PHONE PATCH TO DISPATCH AND MAINT CTL AND ASKED DISPATCH TO VERIFY THAT WE WOULD STILL BE LEGAL TO LAND ON RWY 27 IN SAN USING FLAPS 20 DEGS. WE ASKED MAINT CTL FOR ANY IDEAS THAT MIGHT HELP CORRECT THE PROB. MAINT CTL WAS UNABLE TO OFFER ANY SUGGESTIONS TO 'FIX' THE PROB; AND DISPATCH ADVISED LNDG AT LAX WOULD BE A 'BETTER OPTION.' WE ADVISED ATC OF OUR CHANGE IN DEST AND OUR SIT; AND THEY ASKED IF WE WERE DECLARING AN EMER. WE ADVISED; 'NOT AT HIS TIME!' APPROX 5 MINS LATER ATC ADVISED US THAT THEY HAD DECLARED AN EMER ON OUR BEHALF. WE BEGAN DSCNT A LITTLE BIT EARLY AND AT 7000 FT AND PRIOR TO REACHING SLI; ATTEMPTED TO EXTEND THE LEADING EDGE SLATS USING THE PROC IN THE QRH. WHEN WE SELECTED ALTERNATE LEADING EDGE FLAPS; ALL CAUTION AND EICAS LIGHTS EXTINGUISHED IMMEDIATELY. WE SELECTED FLAPS 1 DEG AND THEY EXTENDED AS EXPECTED. WE GOT ANOTHER PHONE PATCH THROUGH TO DISPATCH; EXPLAINED TO THEM AND MAINT CTL WHAT WE HAD DONE AND WHAT HAD RESULTED; AND WITH THE ADVICE AND CONSENT OF BOTH DECIDED TO PROCEED TO SAN. WE ADVISED SOCAL AND WERE ISSUED A NEW CLRNC TO SAN. WE ALSO CANCELLED THE EMER THAT THEY HAD INITIATED FOR US. WE LANDED IN SAN NORMALLY AND WITHOUT INCIDENT.