A CRJ 200's main landing gear failed to retract after takeoff when the gear handle was raised. An emergency was declared; the QRH procedure completed and the aircraft returned to the departure airport for a normal landing.

Narrative

Took off. I put the gear up when the Captain called for it. Received anti-skid inboard caution message at about 250 FT. 10 seconds later (at about 800 FT) we received master warning; triple chime; gear disagree message. Nose gear had retracted; both main landing gear stayed down. I transferred the radios over to the Captain while I ran the gear disagree QRH. The QRH called for the landing gear manual release to be pulled and then the nose gear came back down and we had all 3 landing gear down and 3 green. The QRH then told us to land at the nearest suitable airport which was the departure airport. Upon completion of the QRH; the Captain transferred the radios back to me. The Captain then advised the Flight Attendant and the passengers that we were returning to the field while I spoke with ATC. They vectored us around for the visual to 18 and the Captain had declared and emergency and had the firetrucks standing by. The approach and landing went smoothly and we had no problems with the gear upon touchdown. We then taxied back to the gate and the crew and passengers were transferred to another aircraft.