select 'alter index '||owner||'.'||segment_name||' rebuild unrecoverable tablespace '||tablespace_name||
' storage ( '||chr(10)||' initial '||bytes||' next '||bytes / 4||' pctincrease '||pct_increase||
' minextents 1 maxextents 100) pctfree 0 ;'
from dba_segments
where owner=upper('&SchemaOwner') and segment_type='INDEX' ;


The Above script will generate a another script , which can be used to rebuild all the indexes in a schema , and you can also use it for single INDEX in a particular schema.

And the Initial extent size would be the present size of the index and with this you will never have extents problem.

And your doubt regarding about the initial extentent is also solved.

test this script in u r R&D box and you can safely implement in production..

Hope this will help you out..

thanks,
Madhu