In tip 6532, I used the following command to un-define 3 environment variables:

for %%x in (user cnt line) do set %%x=

If you need to set a number of environment variables to numeric 0, you could:

for %%x in (var1 var2 var3 var4) do set /a %%x=0

If you need to set a number of environment variables to NO, you could:

for %%x in (var1 var2 var3 var4) do set %%x=NO