you have to apply before you leave the US. It is valid for 2 years and cannot be extended.
http://www.murthy.com/reentry.html
Be aware:
A person who spends most of her/his time abroad and returns only for brief annual visits runs the risk of losing the status. Upon providing valid legal reasons, however, one may be able to obtain a re-entry permit valid for a maximum period of 2 years.
google reentry permit
所有跟帖:
• thanks a lot -flowerpig- ♀ (0 bytes) () 05/18/2005 postreply 13:05:36