A B737-300 FLT CREW ABORT TKOF NOTICING ENG #2 N1 FLUCTUATIONS AT DEN.

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HIGH SPD ABORT DUE TO ENG SURGING. FLT WAS CLRED FOR TKOF. CAPT APPLIED PWR AND PUSHED TOGA. AUTOTHROTTLE SET REDUCED PWR BY 80 KIAS AT WHICH TIME I (THE FO; PNF) CALLED '80 KTS; THRUST SET.' I NOTICED RIGHT AS I WAS MAKING 80 KTS CALL; THAT THE #2 ENG N1 WAS INCREASING 1%-2% OVER THE REDUCED TKOF PWR SETTING. I WAS CONCERNED WITH THE FACT THAT I THOUGHT THE AUTOTHROTTLE WAS INCORRECTLY SETTING TKOF THRUST; AND THAT I KNEW THE MAX PWR SETTING WAS ONLY ABOUT 1% ABOVE REDUCED SETTING. I WAS READY TO PULL BACK THE ENG THRUST; BUT THE N1 IMMEDIATELY STARTED DECREASING. CONTINUING TO MONITOR THE ENG; I BEGAN TO REALIZE THAT IT WAS AN ENG PROB; THAT IT WAS SURGING (N1 FLUCTUATING) AND THAT THE CAPT HAD NOTICED ALSO. HE IMMEDIATELY BEGAN THE ABORTED TKOF PROC BY PULLING THE THROTTLES TO IDLE. MONITORING THE PROC; I NOTICED THE SPD BRAKES WERE STILL DOWN AND I REACHED OVER AND PULLED THEM UP TO THE DEPLOYED POS. EITHER THE CAPT SAID SOMETHING ABOUT TELLING TWR; ON I REMEMBERED MYSELF AND MADE A CALL TO TWR. POSSIBLY THE FIRST CALL TO TWR WAS NOT HEARD; AND THEN WHEN THEY DID HEAR THEY SAID 'WHAT?' AND I REPEATED THE ABORT CALL (TELLING THEM RWY 34R) AND THEY ACKNOWLEDGED MY CALL AND TOLD US TO PULL OFF AND CONTACT GND. WE PULLED OFF; TAXIED TO THE DEICE PAD AND I CONFIRMED THE BRAKE ENERGY AND COOLING TIME REQUIRED. CAPT FOLLOWED HOT BRAKES PROCS (NO PARKING BRAKE; AND SHUTDOWN #2 ENG TO REDUCE BRAKE REQUIREMENTS). WE CONTACTED OPS FOR A GATE; MAINT AND DISPATCH FOR COORD. SUBSEQUENTLY TAXIED TO GATE UNEVENTFULLY.