I would try wiping it with some gun oil and a rag to remove as much rust as possible. Any areas the rust remains take some fine steel wool and gun oil, in a circular motion to prevent pitting. I have also heard Alum Foil in a ball works well, so might want to give that a try. Then wipe down again and fiish with a light coat of oil. The rifle could be used this way, just make sure to wipe it down and re-apply oil often (especially in wet conditions).

The best thing to bring back the rifle is a re-blue by a gunsmith. Suprisingly they aren't real harsh on the pocket book but you may have to wait as they tend to them in batches and in the off season.