First, welcome to the forums. Second, I am very new to bicycle restoration/rejuvenation but I do have a lot of experience with vintage car restoration, those in the know, please correct me if this inappropriate for bicycles.

You will have to clean the area, I recommend bead blasting. With cars, you have three choices depending on the extent of the damage. The preferred method is to fill the pits by using a tig welder and a filler rod. The method is very precise and if you do it well, it requires very little filing. Its best if the steel is at least 20 gauge and you are only doing a few square inches. For bikes, the heat is very precise and if you didn't fill too much at a time and cooled it immediately, it should not effect any brazing.

The next best method is filling with lead. Easy to melt, file and holds paint very well. I don't know how appropriate it would be for a lightweight bike.

The third method is the easiest but loathed by many - bondo. It works fast, it's non-toxic and can be smooth as silk. When it is coved with paint, only you and God know it's there. Similar to bondo is stuff called spray gray. Basically its a thick primer and 3-4 coats will get you .060-080". It sands like bondo.

Good luck with the project. Post some pics