A SF340 engine and propeller were fluctuating after takeoff so the crew declared an emergency and returned to the departure airport.

Narrative

Climbing through 2;800 FT and after completing the climb flow the First Officer noticed a right prop fluctuation of about 90 RPM. I told him we would watch it and continue the departure procedure. A few moments later I too noticed a right TRQ fluctuation of about 10-12% and a slight yawing moment. It occurred again about 30 seconds later. At this time we were being handed off to the next Controller. Before being vectored toward the en-route phase of flight we decided to return to our departure airport. ATC vectored us back. When asked if we where declaring an emergency we decided to answer yes. We where very compressed for time; the airport was not listed as our destination and we were not sure what was wrong with our number 2 engine. We were on down wind to the runway at this point and the engine was running normally. We decided the erratic engine QRC wasn't appropriate. We ran the cruise; decent; and then the approach check list after the First Officer set my instruments for the ILs. Had an uneventful landing and taxied to the gate.