If I leave the us while my extension is pending ,can I return with my visa .USCIS say that if I leave I should return with my receipt.

There is no automatic right to return using a B-1 or B-2 extension receipt. Each entry will be judged on its own merits. The idea of returning with your receipt is to show that you did not unlawfully overstay your period of visit in the US. Such an overstay would automatically invalidate your visa. Due to the limitations of the Lawyers.com Forums, Alan Lee, Esq.'s (the "Firm") participation in responding to questions posted herein does not constitute legal advice, nor legal representation of the person or entity posting a question. No Attorney/Client relationship is or shall be construed to be created hereby. The information provided herein by the Firm is general, and requires that the poster obtain specific legal advice from an attorney. The poster shall not rely upon the information provided herein as legal advice nor as the basis for making any decisions of legal consequence.