FMS PROGRAMMED INCORRECTLY AND ACR GOES OFF COURSE A LITTLE.

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AS PNF; ONE OF MY PREFLT DUTIES IS TO ENSURE THAT THE FMC IS PROPERLY LOADED. ONE ITEM IS TO VERIFY THAT THE CAPT HAS LOADED OUR CLRED RTE. THIS IS OFTEN DONE DURING A SOMEWHAT BUSY TIME WHEN WE ARE DEALING WITH MAINT ITEMS AND FLT ATTENDANT'S NEEDS. OUR FILED RTE FROM SEATTLE TO WASHINGTON DULLES BEGAN WITH: SEA J70 LWT MLS J90 ABR. THE REVISED SEGMENT OF OUR PRE-DEP CLRNC WAS: 'BLUIT3 BLUIT MLP.' BLUIT INTXN LIES ALONG J70; AND THE AIRWAY LEADS TO MLP. A DIRECT ROUTING OF BLUIT TO MLP IS SLIGHTLY N OF THE J70 AIRWAY. AROUND SPOKANE THE CTLR QUERIED WHETHER WE WERE PROCEEDING DIRECT TO MLP. I QUICKLY LOOKED AT THE PDC AND THE FMC AND SAW THAT WE HAD NOT PROGRAMMED THE REVISED ROUTING. ALTHOUGH THE DEV WAS ONLY A FEW MI (AT MOST); THE CAPT HAD PROGRAMMED MLS INSTEAD OF MLP AFTER BLUIT INTXN. THEREFORE; WE WERE HEADED TO MILES CITY (MLS) INSTEAD OF MULLAN PASS (MLP) AFTER BLUIT INTXN. THE CAUSE OF THE ERROR WAS INCORRECT PROGRAMMING AND VERIFICATION OF A REVISED PRE-DEP CLRNC. ALSO; I FEEL THAT THE SIMILARITY BTWN THE DESIGNATORS 'MLS' AND 'MLP' MAY HAVE LEAD TO THE OVERSIGHT. IT IS NOT UNCOMMON TO SEE THAT A REVISED SEGMENT IS ACTUALLY THE ORIGINAL FILED RTE; WHICH MIGHT HAVE LED TO COMPLACENCY.