Though you probably can still keep F1 status, you
still suggest you file I-140 and get I-140 approved first.
there was discussion at
http://boards.immigrationportal.com/showthread.php?t=115661
Someone in this discussion says:
"well, it's certainly an interesting issue. My school's International Center recommends that you maintain F-1 status (by not getting AOS EAD and by not working with it and not travelling on AP) even after you apply for AOS. Also, maintaining full-time enrollment and other attributes of maintaining F-1 status are a must. In this case, they told us, if your I-485 is rejected, you are still in F-1 status and can continue being in it without a need for reinstatement.
They had an information session with INS last year, whereupon this recommendation was offered to my school by INS."