WHY NO U.S. DELEGATION TO HEAR IRANIAN AHMADINEJAD?

I hope to post in the near future. I am still travelling. Access to the net is difficult for me these days. But I am following closely the situation at the U.N. with Iranian president Ahmadinejsad and his speech to the general assembly. What I dont get is why the U.S. delegation was not present for the speech. Instead of bombing Iran let's talk with them.