you have the option to set the compression on the table or you have the option to put compression on the level of a tablespace. If you choose for the tablespace, you set a default for all tables in that tablespace, you can override this default if you need again on table level creation. So if you need all your tables compressed, then choose a tablespace with that default compression specificed, see http://download.oracle.com/docs/cd/E11882_01/server.112/e25494/tspaces002.htm#CIHGCFBB
You'd have to write your own Jobs . Create a list of table names, write a PLSQL block that submits DBMS_SCHEDULER jobs the ALTER TABLE .... commands to rebuild the tables, using a meaningful limit of, say, 8 concurrent jobs.
BTW : I would put in a lot of thought and review before I decided to compress a whole schema or very many tables.
What are the implications on the application ? WHY would one want to compress so many tables ?