when using agents of the oracle, if I have 3 agents can I stack their plus one bonus onto one agent giving one character a plus 3?
thanks in advance for your help.

Sorry, no. The +1 comes from assigning an Agent an action, and that +1 can only be given to the Agent performing said action. From the card:
"...when an Agent is given an action you may choose to give one of its combat values +1..."

thats what i thought, thanks for your help.

Does this action have to be power action or can it be a free action? For example, if a character just uses outwit can his defense be "Oracled" up?

The ICWO +1 is only granted on a non-free action.