i m traveling ouside usa for less than 3 months do i need tranel document?

Yes

If you are FLYING out of the U.S., you must have either a passport or a travel document. How long you will be gone has nothing to do with this. I presume you have a green card...be sure to carry that too. If you do not have a travel document, you can see the site below for application information. There is a customer service number there you may call.

Yes, of course.