Martha,
The Near tool is only available with an ArcInfo license for Desktop. There are 3 licenses: ArcView, ArcEditor, and ArcInfo. Your post doesn't say which one you have, but that is the proper message if you indeed don't have an ArcInfo license. The Near 3D tool will of course require a license for 3D Analyst regardless of your license for ArcGIS Desktop. Every geoprocessing tool shows you the required license level in the documentation.
Best Regards,
Eric