PLT OF A C172 FLEW INTO RESTR AIRSPACE WHEN BECOMING DISORIENTED DUE TO DETERIORATING WX CONDITIONS.

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CROSSED THE SUSQUEHANNA AT 1800 FT AND DIRECT MTN. THE WX AT MTN WAS RPTING 1700 FT AND 3 MI VISIBILITY. THE CEILING STARTED TO DROP SO I STARTED A GRADUAL DSCNT IN ORDER TO MAINTAIN VFR. I CONTACTED MTN TWR 10 MI NW OF THE ARPT AND AT 800 FT IN ORDER TO MAINTAIN CLOUD CLRNC. CONTINUED INBOUND UNTIL THE CEILING DROPPED QUICKLY PLACING US AT 500 FT TO MAINTAIN CLOUD CLRNC. AT THIS POINT I STARTED TO TURN THE ACFT AROUND TO HEAD BACK THE WAY WE CAME. THE PLT IN THE R SEAT; WHO HAD HIGHER HRS AND MORE EXPERIENCE OFFERED TO TAKE THE CTLS. HE TURNED THE ACFT 30 DEGS TO THE L TO AVOID LOWER CLOUDS AND CONTINUED INBOUND TO MTN. A FEW MINS LATER WE LOOKED DOWN TO SEE PHILLIPS AIRFIELD. REALIZING THAT WE WERE IN A RESTR AREA (R-4001A) I WENT TO GRAB THE YOKE TO TURN US AWAY FROM THE RESTR AREA; BUT THE OTHER PLT HAD ALREADY STARTED TO TURN. AT THIS POINT THE CTL TWR REQUESTED OUR HEADING AND RPTED THAT WE WERE IN THE RESTR AREA. I TOOK CTL OF THE ACFT AND DIVERTED TO ANOTHER ARPT DUE TO THE DECREASING CONDITIONS AT MTN. FOR THE FUTURE I WILL BE MORE CAUTIOUS OF TURNING THE CTLS OVER TO ANOTHER PLT. THE FIRST THING I SHOULD HAVE DONE IN THIS SIT WAS TURN THE ACFT AROUND AND HEAD FOR BETTER CONDITIONS. AFTER THAT I COULD HAVE EITHER DIVERTED TO ANOTHER ARPT OR CONTINUE THE TRIP IFR AND SHOOT AN APCH IN TO MTN.