Suppressing duplicate key error messages in postgres log?

Hi

I have a postgres table which relies on a unique index to act as a
semaphore to share a resource among many competing processes on several
different servers. This table is hit multiple times per second. The
postgres log is being filled by millions of messages of the sort
ERROR: Cannot insert a duplicate key into unique index ...

Is there any way to suppress this message so that it won't appear in the
log? I looked at the documentation and log_min_error_statement looked
promising. I set it to panic, but the messages continue. What am I doing
wrong?

Thanks in advance for any assistance

Larry