Sample Research Grant White Paper
Based on a little Googling, his white paper sounds like a preproposal. It is likely a short overview over your research project: the problem you are working on, your approach to solving it, how much it will cost, and what you and/or the agency will get out of it. Consider this white paper an outline of your full proposal.

Many agencies will ask for these if they expect a particular program or funding opportunity will have a high response or if the purpose of the program is to provide a single large award to one project. The prepreposals are used to narrow the field before they ask for full proposals from a smaller set of submitters. 

I have not been successful at finding examples, since proposals and affiliated documents are almost never released unless they are funded. However, I have found some tips for preparing white papers from Rochester Institute of Technology and Purdue.