As metadata is not exposed by REST endpoints the only way to work with metadata is by using Arcobjects or SOAP through a dot net web service. If you have questions on doing that they will be best answered on the forums that are specific to those technologies.
there is even no way you do, for example: is it possible to expose services (geoprocessing) metadata via ArcGIS Server in version 10? or by using python script that you can also publish scripts on the ags?