The first! Although I don't really see the need for "in the process of". I'd say "I'm working" or "I'm in the process of + name of task e.g. typing a letter.
We usually use "work in progress" as a noun to describe an on-going project.
Perhaps you are confusing what you want to say with the noun phrase work-in-progress (with or without hyphens) meaning a project which is still being worked on, but may take a long time. It is progressing, but the end is not in sight. (This would preclude using it with "soon".)
I prefer your first sentence, but usually working would be followed by "...on [name of what you are working on]" or at least "...on it", if it is clearly what is under discussion.
For formal use, I would leave out all reference to working (it sounds like an excuse) and just say, "I will present it/let you know/deliver it soon" or "...when it is ready/finished" or "...by Tuesday".