We are really using Solaris rather than a Linux distro, but I'm wondering if there is a means more specific to Apache to get it done.

I do not fully realize how to start by using it past a couple of exec'd instructions in PHP. (prstat -avm 1 1 grep webservd tail -1)

Some additional information - I am regrettably within an old atmosphere without a penny that even slightly resembles load balancing, so I must make my very own...

I do not think there's any Apache-specific way.

I remember when i authored a cron job that checked CPU strain on each run and left if over a certain threshold. You can run the check above, and when load is high output a 5xx status as well as an error. Something similar to:

$load = exec('prstat -avm 1 1 | grep webservd | tail -1');
if($load > $threshold) {    
    header('HTTP/1.1 503 Service unavailable - server load too high');
    die('Load is too high');
}

(I am unsure the format from the creation of prstat)