Can I enter US on OPT while my H1B is under processing?

[mohitunlimited]

I am an F1 student and just graduated this spring. I am currently not in US .Due to some communication gap, my employer filed for Form I-129 after I left US. I left US on 13th May 2012 and my H1B petition form was filed on 23rd May 2012. I was planning to start my job on July 9th 2012.

My OPT Start date is 20th June.

I wanted to know if I can enter US on OPT while H1b petition is under processing.?. If not what are the necessary steps I should take to re enter US