* Eye resolution to censure Iran at 35-nation IAEA meeting
* Need diplomatic progress to avoid any Israeli military action
* Islamic state denies bomb aims, expands enrichment capacity
By Fredrik Dahl
VIENNA, Sept 11 (Reuters) - Six world powers at a U.N. nuclear meeting are set to voice deep concern about Iran's expanded uranium enrichment and urge it to open up to investigations, diplomats said on Tuesday, in search of a breakthrough to head off a risk of Israeli military action.
They said the United States, Russia, China, France, Britain and Germany had agreed a joint text on Iran's nuclear programme that could be submitted as a resolution to this week's meeting of the 35-nation governing board of the International Atomic Energy Agency (IAEA), or take the lesser form of a statement.
It was meant to reaffirm big power unity on the matter, whether or not they achieve a resolution rebuking Iran over its defiance of international demands to curb activity seen by the West as a disguised effort to develop nuclear arms capability.
The text expresses particular concern about Fordow, an Iranian enrichment site deep underground where an IAEA report in late August said the Islamic state had doubled its capacity over the last three months, the diplomats said.
If it becomes a resolution with wider support among IAEA board members meeting in Vienna, that would be welcomed by Western diplomats, who have been searching for means to crank up international pressure on the Islamic Republic.
Tehran says its enrichment programme is peaceful, aimed at producing electricity and not bombs. Refined uranium can be used to fuel nuclear power plants. If enriched to a high degree, it can provide the explosive core for a nuclear warhead.
The fact that the six powers were able to hammer out a joint text underlined their desire to maintain unity over the long-running dispute, which has the potential to plunge the Middle East into a new war.
The world powers are all involved in a diplomatic push to resolve the nuclear dispute peacefully that has made little headway since high-level talks with Iran resumed in April.
Israel, believed to be the only nuclear-armed state in the Middle East, sees the chance of Iran developing an atomic bomb as a mortal threat and, running out of patience with diplomacy and sanctions, has stepped up hints of military action.
Israeli Prime Minister Benjamin Netanyahu on Tuesday ramped up threats to attack Iran, saying if world powers refused to set a red line for Tehran's nuclear programme, they could not demand that Israel hold its fire.
Western states reason that intensifying pressure on Iran "may deter Israel from taking the matter into its own hands" before the U.S. election in November, nuclear proliferation expert Mark Hibbs of the Carnegie Endowment think-tank said.
After the U.S. presidential vote, "Israel's leverage over the U.S. will dramatically end and Iran can resume negotiating because it knows who's in the White House," Hibbs said.
China and Russia have supported a series of U.N. Security Council sanctions rounds imposed on Iran since 2006.
But both Beijing and Moscow have sharply criticised unilateral punitive steps by the United States and its allies to block the Islamic Republic's oil exports, and diplomats said the two were sceptical about the need for an IAEA resolution.
The text agreed by the six powers expressed continued support for diplomatic efforts aimed at a peaceful resolution of the row over Iran's atomic ambitions, one diplomat said.
It also stressed their backing for the IAEA's efforts to clarify concerns about possible military dimensions to Iran's nuclear programme. The IAEA is investigating suspected atomic bomb research but the inquiry has made scant progress since 2008 because of Iranian stonewalling of requests for access.
IAEA head Yukiya Amano pressed Iran on Monday to grant his inspectors immediate access to the Parchin military site, where they believe Tehran may have conducted explosives tests relevant to the development of nuclear weapons.
If Iran decides to make a nuclear weapon, the United States would have a little more than a year to act to stop it, U.S. Defense Secretary Leon Panetta said on Tuesday.