AN EMB135 PILOT REPORTS AN ALT DEV CAUSED BY THE CREW'S DISTRACTION ABOUT FUEL WHEN AN UNSCHEDULED ARR DELAY CAUSED GREATER THAN EXPECTED FUEL BURN.

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WHILE FLYING FROM ZZZ1 TO LGA WE WERE GIVEN HOLDING INSTRUCTIONS AT ABC INTXN AT 12000 FT. THE CAPT WAS CONCERNED ABOUT FUEL AND TOLD ME TO TAKE THE ACFT. WE WERE AT FL190 AT THAT TIME. DURING THE DSCNT I WAS ALSO TALKING TO ATC AND BECAME DISTR AND DIDN'T CALL OUT THE DSCNT CHKLIST. UPON ARR AT THE HOLDING FIX AND TURNING OUTBOUND ATC TOLD US TO CHK OUR ALT AND ALTIMETER. WE WERE STILL AT 29.92. WE CHANGED THE ALTIMETER TO 30.42 AND REALIZED WE HAD BEEN 400 FT OFF TARGET ALT. WE THEN ASKED ATC IF THIS HAD CAUSED A PROB AND THEY SAID 'NO.' THE CAPT AND I DECIDED THAT; EVEN THOUGH ATC SAID IT WASN'T AN ISSUE; WE WOULD GO AHEAD AND SEND IN A RPT. IF WE HAD BEEN GIVEN A BETTER FUEL LOAD AT ZZZ1 THIS WOULD NEVER HAVE HAPPENED. THE CAPT WOULDN'T HAVE HAD TO MAKE PLANS FOR A DEV AND WE WOULD HAVE REMAINED A 2-MAN CREW. WE WERE ALL READY TO DIVERT TO PHILADELPHIA TO GET MORE FUEL WHEN ATC CLRED US DIRECT TO LGA. HAD THE FLT PLANNING INCLUDED MORE NECESSARY FUEL FOR GOING INTO NYC AIRSPACE WE COULD HAVE AVOIDED THE SITUATION. HAD I NOT BEEN OVERWHELMED; TASK SATURATED; AND DISTR AT THE TIME OF THE DSCNT I WOULD HAVE BEEN FOCUSED ENOUGH TO PERFORM THE DSCNT CHKLIST AT THE PROPER TIME. HAVING THIS HAPPEN TO ME HAS MADE AN IMPRESSION THAT WHEN I AM FEELING OVERLOADED I NEED TO TAKE EVEN JUST A COUPLE OF SECONDS TO CHK OUT AND EVALUATE THE SITUATION AND BE SURE EVERYTHING IS DONE THAT NEEDS TO BE ACCOMPLISHED.