I'd suggest reading Mythical Man Month and then going to talk with the program manager. You can point out that it will take more time to bring all these new people on board rather than continuing to build out the project yourself. The book should provide you with a bit of ammunition.
It does sound like the program manager is trying to get his/her name associated with the project, ie riding on you coat tails. There isn't anything particularly wrong with this, but it requires you to manage the resource rather than becoming managed by their "help" If you don't have the skill to do so, you will need to find a mentor to give you advice. Most large companies operate as much on politics as they do on actual products. Solicit advice from senior engineers and others that you feel have the knowledge and skills to work in the political landscape. Not much else I can tell you.