* IAEA probe into suspected Iranian bomb research stalled * West says Tehran must step up cooperation with U.N. agency * But **t realistic to expect "confession" - diplomats (Adds U.S. official comment, paragraph 4, edits) By Fredrik Dahl and Louis Charbonneau VIENNA, **v 22 (Reuters) - World powers are pressing Iran to stop stonewalling a U.N. atomic bomb investigation as part of a wider nuclear accord, but look likely to stop short of demanding full disclosure of any secret ****** work by Tehran to avoid killing an historic deal. ...