wait. that little tom kyte devil on my shoulder tells me you need more of an answer than just "yes"...

First, if this expansion is due to normal activity, then you can shrink the tablespace but it will grow right back to it's current size.

If this is due to abnormal activity, then you can assign all the users that use that TS to a new temp ts, drop the tempfile with "alter database tempfile 'xyz.dbf' drop;", rm it from the OS, recreate it the size you want with "alter tablespace temp add tempfile 'xyz.dbf' size 1m autoextend on next 1m maxsize 4096M;", and re-assign the users back.