By Arshad Mohammed WASHINGTON, Oct 23 (Reuters) - Iran will be widely seen to be responsible if a comprehensive deal to curb its nuclear program in exchange for sanctions relief is **t reached, the top U.S. negotiator said on Thursday. U.S. Under-Secretary of State Wendy Sherman also said major powers negotiating with Iran have offered it ideas that are "equitable, enforceable and consistent with Tehran's expressed desire for a viable civilian nuclear program." Britain, China, France, Germany, Russia and the United States are seeking to reach a deal with Iran by **v. 24. ...