is it ethical to publish the same paper in a conference proceedings and a journal? The papers for a conference are limited to 3 pages. On the website, however, it says Transactions of the IEEE offers a special feature edition (whatever it means?), so I think it would be good to submit the full manuscript to this special issue. 
But that means I'm submitting two papers with the same title to a journal and a conference proceedings. 
Is that ethical? How should I deal with this?



The extended abstract is accepted. Meanwhile the special issued journal is open for submission. I contacted the editor of the journal and she said you can present your longer version in the transaction journal.

But basically I think I will use the same text and figures. Maybe 2 more pages than the conference one. Is it considered as self-plagiarism ?
In computer science, the typical rule of thumb is that a conference paper may be 'upgraded' into a journal paper with at least 30% new material.  Certain subfields and other related fields covered by the IEEE may have different standards, however, and ultimately, the standard for this particular conference/special-issue pair is whatever the organizers have decided it is.  Since a 3 page paper is a very short form, though, the full manuscript will almost certainly be reasonable to submit to a journal.

It may not, however, be appropriate to submit to this special issue. Special issues associated with conferences are sometimes open submission (in which case, you can probably submit immediately), sometimes open to extended versions of any accepted papers (in which case, you need to wait to see if your paper is accepted), and sometimes only for a select set of invited papers (in which case, you need to wait to see if you are invited).  The organizers should have posted this information on their site: if they have not, you can email them to ask.