VIENNA (Reuters) - The chief of the UN nuclear watchdog will tell nations on its governing board this week that Iran's pledge of atomic transparency should be given a chance to work, not dismissed as a time-buying ruse.

An ambiguously-worded deal Iran agreed with International Atomic Energy Agency inspectors to explain the scope of its nuclear program faces scrutiny at a meeting of the IAEA's 35-nation board starting on Monday.
The plan has vexed Western powers by allowing Iran to answer questions one by one according to a timeline.
It has also wrong-footed a U.S.-led push to rein in Iran by eroding European support for, and stiffening Russian resistance to, tougher UN sanctions. Iran won the reprieve by threatening to cut off the IAEA if pressure intensifies, diplomats said.
After sparring with Washington over the plan and receiving a demarche from its closest EU allies, IAEA Director Mohamed ElBaradei said he would underline to the board that the deal marks an important step forward, not a damaging setback.
Western delegates said they were looking for ElBaradei to correct impressions left by the plan's text that the IAEA could make no more inquiries once questions were solved even if fresh suspicions arose, and excused Iran from UN demands to grant wider inspections or suspend enrichment.
ElBaradei said those perceptions were indeed incorrect. ""There has been quite a lot of misunderstanding,"" he said.
The plan is a ""working document"" to be built on, not a final treaty that precludes any measures not spelled out, he told reporters invited to a rare briefing on Friday.
He said he would also make clear the IAEA would insist on documentation and access to hitherto off-limits areas to check Iranian answers, a key measure missing from the plan.
""Whether Iran will walk out of this understanding, I don't know now. All we know is that Iran has committed to cooperating and clearing their name. We have to give them that chance.""
----------U.S. softens criticism
Gregory Schulte, U.S. ambassador to the IAEA who at first suggested agency negotiators had been outfoxed by Iran, said on Friday the plan had potential merit.
Iran says its nuclear energy quest is solely for electricity generation, not a front for bombmaking as the West claims, and it is serious about going the extra mile to overcome mistrust.
Western diplomats said ElBaradei had privately assured them he would judge by November, when the board holds its year-end meeting, whether Iran was serious. If not, that would help create a basis for a third, stronger sanctions resolution.
ElBaradei said he predicted broad support for the plan at the board gathering once he clarified its dimensions