By Parisa Hafezi and Louis Charbonneau ANKARA/NEW YORK, Oct 21 (Reuters) - Iran is pushing what it portrays as a new compromise proposal in nuclear talks, but Western negotiators say it offers ** viable concessions, underscoring how far apart the two sides are as they enter crunch time before a **v. 24 deadline. In the negotiations with six major powers, the Iranians say they are ** longer demanding a total end to eco**mic sanctions in return for curbing their nuclear program and would accept initially lifting just the latest, most damaging, sanctions. ...