Put all those settings into a LOGIN.SQL file (which should be in a directory you use when connecting to SQL*Plus). Alternatively, to use it always, create a GLOGIN.SQL file ("global") (it should be located in your ORACLE_HOME\SQLPLUS\ADMIN directory).
Thanks! for the info ....i did some google found some more info..
Actually i am working on a remote machine and i dont have access to Oracle installation directory.i.e ADMIN etc
So i have stored the current setting into a file using STORE SET FILE_NAME which stores all the env variables and then i modiefied the variables . On logging to a new session i can use START FILE_NAME TO use the new settings.