I agree with Saje - he needs to find some confidence and some of this needs to be his choice. If he's pushed, I expect he might react by biting.
Dogs develop most of their personality by a few months old, and those are the months that are the prime time to socialize. Right now you're going to be working against his fears and it won't be easy.
You'll need to carefully control his situation and try not to put him under too much stress or in a place where he thinks that he has to defend himself. But you also need to find a way to really praise him whenever he offers even the slightest confident move. This may be as little as seeing a person in the distance and not reacting - praise and treat! If you go a foot closer towards the distant person and he doesn't react - praise and treat! It has to be that small of a behavior in order to start building his confidence. I would be willing to bet that when he's in fear mode he doesn't give many confident moves and so you need to start with those fearful things a long ways away.
If you do end up in a situation where he pulls back and barks, you don't want to stand in front of him (unless you feel that's the only way to keep someone from getting bit). By standing in front of him, you are "protecting" him from the fearful thing and feeding into his thoughts that there is a reason for the fear. You can't give him any sort of reaction that makes him think his fear is justified - no reassurance, no scolding, no commands, no attention. At that point in time, he will take those as reinforcement for his behavior.
Desensitization takes a long long time. There is no easy cure. If you start by rewarding at a distance and gradually (over a period of months) move closer you may be able to work through his fears. But as long as he's put into a position where he feels he has to act fearful, the problem will just continue.
If there is a behaviorist in your area (a true behaviorist) or a trainer who works with 100% positive methods (don't use them if they want to put a corrective collar on him or scold or use harsh techniques) then I would really recommend that you get him assessed and they should be able to set you up with desensitization techniques.
Good luck with him - it's not an easy task but it CAN be done!
Melanie and the gang in Alaska