Try Evapo-Rust.

It will remove the rust without harming the underlying metal. It will also remove any blueing, not sure about parkerizing.

All you do is soak the clip (or other item) in Evapo-Rust for anywhere from 30 minutes to 24 hours and the rust is gone. Then rinse in hot water and dry it off. It's that simple!
It's fantastic stuff... I use it a lot (restoring helmets, entrenching tools, bayonets, tools, cast iron, SMLE charger clips, etc.)

Check out their web-site for more info... Evapo-Rust rust remover description page

Hope this helps.