chmod problem

[John Gatewood Ham]

On Linux with coreutils 6.9, glibc 2.3.6, kernel 2.6.22.6, bash 3.2.35
I can do this:

#umask
0022
#mkdir testme
#chmod 02700 testme
#ls -ld testme
drwx--S--- 2 root root 4096 Sep  5 16:21 testme
#chmod 0700 testme
#ls -ld testme
drwx--S--- 2 root root 4096 Sep  5 16:21 testme

I was under the impression 0700 was the octal code and would thus
result in 0700 permissions, not leaving 2700 permissions.  How
can I use the octcal code to get 0700 permissions for a directory
with 2700 permissions?  I tried 00700 but that didn't matter.  I know
I can do 'chmod g-s testme' but since I can set the setgid flag
with octal codes I would like to be able to unset the setgid flag
with octal codes as well.  I was able to achieve this in 2 steps
with 'chmod 0 testme' followed by 'chmod 0700 testme'.  Can it be
done in 1 step using an octal number?

JGH