Substitutions [Moved from Minneapolis St Paul]
For future reference - these sorts of questions should be on the home cooking board instead of one of the city-specific boards.
As for your question...it will not be an exact substitute (tomato sauce is much more liquid than tomato paste). However, if your recipe has other liquid, you could probably cut down on the other liquid by ~1/2c. and use the tomato sauce (although the "intensity" of tomato flavor will not be quite as high).