Can I apply h4 meanwhile h1 exteniton in process

Dear Saurabh/Kumar

I have h1b extention in process , while my i94 has been already expired, if my H1b rejected, I will be out of status , Please advise , can I apply H4 (after H1 rejection within 30 day grace period time without leaving the country if h1 rejected) as my spouse is having h1 , or can we parallelly apply h4 right now and withdraw h4 later.