JERUSALEM » For Israel and Persian Gulf states like Saudi Arabia, President Barack Obama’s historic telephone call with President Hasan Rouhani of Iran on Friday was the geopolitical equivalent of discovering your best friend flirting with your main rival.

Although few nations have a greater interest in Obama’s promise to stop Iran from developing a nuclear bomb, his overtures to Rouhani were greeted with alarm here and in other Middle East capitals allied with the United States. They worry about Iran’s sincerity, and fear that Obama’s desire for a diplomatic deal will only buy Iran time to continue a march toward building a nuclear weapon.

But beyond that, the prospect of even a nonnuclear Iran – strengthened economically by the lifting of sanctions, and emboldened politically by renewed relations with Washington – is seen as a dire threat that could upend the dynamics in this volatile region.

One gulf academic in a Twitter post likened the phone call to "the fall of the Berlin Wall." An Israeli lawmaker said in a radio interview that he hoped Obama would not be the next Neville Chamberlain, known for appeasement of the Nazis in 1938.

"There is a lot of suspicion and even paranoia about some secret deal between Iran and America," said Jamal Khashoggi, a prominent Saudi journalist who is close to the royal family. "My concern is that the Americans will accept Iran as it is – so that the Iranians can continue their old policies of expansionism and aggression."

Saudi Arabia and the other Sunni-dominated gulf countries share a concern about a shift in the balance of power toward Iran’s Shiite-led government and its allies. For Israel, Iran remains the sponsor of global terrorism and of the Lebanese militia Hezbollah and the Palestinian militant group Hamas, both avowed enemies of Israel’s existence.

"They can change the regime, but one thing won’t change and that is the hostility against Israel," warned Uzi Rabi, chairman of a Middle East studies center at Tel Aviv University. "Part of the plan is to drive a wedge between Americans and Europeans and Israel. I hate to say it, but what the Iranians managed to do is to change the whole game."

There was no official reaction Saturday from Riyadh or Jerusalem to the telephone call, which was the first direct conversation between U.S. and Iranian presidents in more than three decades. Prime Minister Benjamin Netanyahu of Israel spent the day rewriting the speech he is scheduled to deliver Tuesday at the United Nations and preparing for a meeting Monday with Obama. After years in which Netanyahu exploited Iran’s nuclear ambitions to rally the world against Iran and force its isolation, Israel could find itself increasingly isolated in its hard-line stance.

"Netanyahu understands that there is a lot of euphoria," a senior Israeli official said. "Netanyahu knows that people in the international community will want to believe. I think you’ll see in his remarks a lot of facts, a lot of facts that no one denies."

The official, who spoke on the condition of anonymity because he was not authorized to do otherwise, and Yuval Steinitz, Israel’s minister of strategic affairs, declined to discuss the phone call.

"The main thing is not procedures but substance," said Steinitz, who led Israel’s delegation in a boycott of Rouhani’s U.N. speech. "The most critical problem with Iran is its aim of achieving nuclear weapons, but the problem with Iran is wider," Steinitz added. "Iran is not a peace-seeking country or regime – on the contrary. Iran is maybe the most aggressive country in the world, and it’s not just against Israel."

Saudi Arabia and other gulf states view Iran as a regional nemesis whose nuclear program is only one element of a broader effort to project power. The rivalry is made more bitter by the sectarian dimension, and competition over supplying oil to the world. The Saudi leadership has long been uneasy with Obama’s handling of the Arab uprisings that began in 2011, which it sees as a threat to the regional order. The president’s overtures to Iran add to a growing impatience and exasperation among Arabs in the gulf over Washington’s retreat from threats to strike Syria, whose civil war is viewed as a proxy for the larger sectarian and strategic battle unfolding across the region.

"The gulf states, and the Iranians, still see this as a balance-of-power struggle," said Salman Shaikh, director of the Brookings Doha Center. "And Obama’s warning and Rouhani’s charm offensive, as well as what they would see as a hoodwinking of the United States on the nuclear issue, could have far-reaching consequences on the balance-of-power struggle."

Mustafa Alani, a Dubai-based security analyst, said the Saudis think that Obama is "not a reliable ally, that he’s bending to the Syrians and Iranians." Mishaal al-Gergawi, a political analyst based in the United Arab Emirates, said, "There is a lot of cynicism, and it feeds into the notion that Obama is very naove – he was naove with the Muslim Brotherhood, naove with Bashar al-Assad, and he is now naove with Iran."

Israeli analysts, too, worry over what they see as the Obama administration’s weak and wavering policies toward the Middle East. After the Syrian chemical weapons crisis, some said the phone call only upped the ante for a diplomatic victory that could lead Washington to accept what Jerusalem would consider a "bad deal" with Iran, which insists its nuclear program is for civilian purposes only.

"Obama is interested in showing foreign-policy success because he hasn’t had too many of them," said Emily Landau, an Iran expert at the Institute for National Security Studies in Tel Aviv. "I’m afraid that for the sake of that he might be willing to compromise on the nuclear issue in a manner that I think is detrimental to U.S. national security interests, leave aside Israel."

Landau was one of several Israeli analysts who urged the world to focus not on Rouhani’s statements in New York but the continued nuclear activity in Iran. She pointed to a Sept. 12 letter that Iran sent the International Atomic Energy Agency with 20 pages of complaints about its investigation as a sign that nothing had changed. She and others also noted that Rouhani was Iran’s nuclear negotiator in a 2003 deal it later violated; several Iran experts have seized on a speech he gave then emphasizing the importance of enrichment ability for weapons-grade uranium as political leverage.

Rouhani "confirmed the assessment that Iran had used the calm atmosphere of negotiations as a smokescreen behind which it continued to deliberately advance its nuclear program," wrote Chen Kane, a senior research associate at the James Martin Center for Nonproliferation Studies in Washington. The speech reinforced the view that Iran’s "main objective in negotiating" she said, "was simply to gain time."

The skeptics’ main concern now is that four to six months of negotiations would allow Iran to get to the breakout point for developing a bomb.

"It’s not just that forever we go on with an Iranian nuclear program that never reaches conclusion, it’s that diplomacy can be a way of helping it get to the finishing line," cautioned Jonathan Spyer of the Interdisciplinary Center in Herzliya. "The last week of diplomacy in New York has really created the impression that a very, very different understanding of what’s going on here, and what is potentially on the table, exists between the U.S. administration and the Israel government."

Yoel Guzansky, who handled the Iranian nuclear file for the Israeli prime minister’s security council from 2005 to 2009, said the new momentum for nuclear talks with Iran had "sidelined" Israel as "a potential spoiler."

"You can’t do anything while Iran and the U.S. are talking; you’ll just be someone who is destroying the last chance for peace," Guzansky said. "If there is a change of tone in Iran and Washington, Israel should also change the tone. If there is a deal we embrace it, we support it, but show us the details."

© 2013 The New York Times Company