m3u files cant directly support smart playlists - they are just a list of files. What i can do is allow you to save the smart playlist as a m3u file.
Currently the only way i can think you can acheive this is to create a new playlist, and then drag the files from the smart playlist into the new playist.
The new playlist will be a m3u file located in the Playlists sub-folder of your library