You can ask the AI to attack/defend a location.
Unforetunately it only takes your request under advisement, and may, or may not do it.
Even worse, if you and the AI have numerical supremacy, it will still retreat if it's fleet is smaller then the enemies (AI is chicken $h!t). So your #1 rank fleet gets worked by #2 and #3 while the AI with #4 retreats, even if 1+4> 2+3..
I hope this is addressed in 1.1 - the AI should look at ALL allied ships, not just own vs enemy when deciding what to do!!!