My 2c's:

I am not sure if I understood Suresh's posting clearly or not. However as I understood what he wants to know is "how to turn off archiving WHILE import is GOING ON".
Having said that, when Suresh said that the init.ora file was modified and the DB bounced, I assume that it was done with the abort option (otherwise it can't be done right? the import is still going on!).
So, the the DB was restarted, oracle was doing instance recovery (must have been a large table which was being imported) and so it seemed that the DB had hung.
As far as setting archiving off, Jeff has already pointed out what to do.

-amar