(Reuters) - Defense Minister Ehud Barak restated Israel´s fears of a nuclear-armed Iran on Thursday after his top general clashed with the government´s line by describing the Islamic republic as "very rational" and unlikely to build a bomb.

Addressing foreign diplomats on Israel´s independence day, Barak said Iranian leaders were not "rational in the Western sense of the word - connoting the quest for status quo and the peaceful resolution of problems".

Believing otherwise "borders on blindness or irresponsibility", said Barak, who branded Iran, with its religiously fuelled calls for the Jewish state´s demise, as seeking regional hegemony and being "undeterred by the apocalyptic".

While the speech reiterated international concerns that Iran´s civilian uranium enrichment program has secret military designs, and Israel´s readiness to attack its foe pre-emptively, some of the language was unusually strong for Barak. A transcript circulated to the media had key passages underlined.

Another official told Reuters that Barak wanted to "set things straight" after Israel´s military chief, Lieutenant-General Benny Gantz, said in a newspaper interview that Iran - which insists its nuclear ambitions are peaceful - was preparing components of a bomb but was unlikely to "go the extra mile" of assembling it, given the likely global backlash.

"I think the Iranian leadership is composed of very rational people," Gantz told the liberal Haaretz daily on Wednesday.

Barak´s speech did not mention Gantz specifically. Unlike in previous years, the event was closed to the media, though that decision was taken before the general´s interview was published.

BLEAK ON BAGHDAD

In lobbying world powers to stiffen sanctions designed to curb Iran´s uranium enrichment, Israel has long appealed to their worries about Middle East destabilization and oil shock.

This has entailed warning that an Iranian bomb would embolden Islamist militants, spark arms races, and rattle energy markets. It has also entailed hinting that Israel - assumed to have the region´s only atomic arsenal - could go to war to thwart what it regards as a mortal threat should it deem that foreign diplomacy with Tehran is at a dead end.

Six world powers revived negotiations with Iran in Istanbul last month and are due to resume them in Baghdad on May 23.

Barak was pessimistic about the talks, saying Iran was buying time in order to dig in behind defenses that would allow its nuclear facilities to fend off aerial attack.

"The sanctions today are harsher that in the past," he said. "But the truth must be told. The chance that, at this level of pressure, Iran will meet the international demand to stop the program irrevocably - that chance appears to be low."

During Israel´s Holocaust remembrances last week, Prime Minister Benjamin Netanyahu said Iran was "feverishly working to develop atomic weapons" to use against his country.

Speaking on CNN on Tuesday, Netanyahu said he would not want to bet "the security of the world on Iran´s rational behavior". A "militant Islamic regime", he said, "can put their ideology before their survival".

The portrayal of Iran as irrational - willing to attack Israel with a nuclear weapon even if it means inviting catastrophic retaliation in kind - could bolster a case for pre-emptive bombing to take out its atomic facilities.

The United States has also not ruled out military action as a last resort. But many allies of Washington, and even some senior U.S. officials, fear such an attack could ignite a broader war while only delaying Iran´s nuclear advances.

Gantz´s assessment appeared to be in step with the view of his U.S. counterpart, General Martin Dempsey. He said in a CNN interview in February that he believed Iran was a "rational actor" and it would be premature to take military action against it. (Writing by Dan Williams; Editing by Kevin Liffey) (© Thomson Reuters 2012. 04/27/12)