[Calacirya]

Originally Posted by Sarumian

If I recollect it correctly, somewhere in Silmarillion Tolkien says Sauron was the most powerful of all Maiar. I agree, that Sauron have wasted quite a lot of his power by the time of the War of the Ring but still was very potent.

I do not recall this being said at all. What you may be remembering is:

Sauron, greatest and most terrible of the servants of Morgoth

...which is from the Silmarillion, but does not imply that Sauron is the most powerful of the Maiar.

Never the less, you are correct in assuming that is powers would be diminished, especially if his powers worked in a similar way to Morgoth (the more evil he put forth, the less power was left to he himself).