Conditional variables (?)

Hi, 
I would like to set up my project to use the following two cases:
1. I run/debug the project on my system
I would like the variable debug=1, and use the web.config in the project
2. I run the compiled version from the published web site
I would like the variable debug=0, and use the alternate web.config (web.production.config)
Is there any way to do this manually?
 
Cheers!
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