LOS ANGELES — Israeli and U.S. politicians lately have been bandying about the prospect of an airstrike on Iranian nuclear facilities, stirring fear that another destabilizing clash could be provoked in a region already rife with civil war in Syria and other religious and political tensions.

But nonproliferation experts and Middle East analysts are skeptical of Israeli claims that the Tehran regime is so close to building a nuclear weapon that time is running out for a peaceful resolution of the decades-long standoff.

“This is a window that has been closing for 15 years now, and it’s always imminently about to close,” said Jamal Abdi, policy director for the National Iranian American Council. He sees the sudden flurry of diplomacy between Jerusalem and Washington as an outgrowth of the U.S. presidential campaign and Israeli interest in ensuring that the United States continues to hold a hard line against Iran.

U.S. Defense Secretary Leon E. Panetta was in Jerusalem on Wednesday to urge Israeli leaders to let negotiations and sanctions do their work before unleashing any military strike at facilities where Iran is suspected of enriching uranium or storing the processed fuel for potential upgrading to weapons’ quality.

His visit followed one Sunday by Mitt Romney, the presumptive Republican presidential candidate who put the political spotlight on tension between the nation and Iran by promising to “respect” any decision Israel’s leadership takes to protect itself.

The high-profile visits gave a platform to Prime Minister Benjamin Netanyahu to proclaim Israeli impatience with diplomacy and sanctions, which he claimed had “not set back the Iranian program by one iota.”

Netanyahu complained that “however forceful our statements, they have not convinced Iran that we are serious about stopping them.” He put Panetta on notice that Israel is prepared to act alone in attacking Iran if it perceives itself to be at risk.

Alon Ben-Meir, a professor of international relations at New York University’s Center for Global Affairs, said Netanyahu and Israeli Defense Minister Ehud Barak used the American visits to send a message to Tehran that Israel won’t hesitate to take unilateral action.

Ben-Meir cautions U.S. and other officials against seeing the Israeli threats as mere posturing, pointing out the profound national security concerns that shape Israeli defense policy and the country’s unshakable faith that Washington will come to its rescue if a strike against Iran triggers retaliation by Tehran or its well-armed allies in the Lebanon-based Hezbollah militia.

“I don’t think Israel is bluffing entirely. There is an element of exaggerating its readiness to act and likelihood of winning. But many advisers to Prime Minister Netanyahu are saying that if he waits six or eight months, they may end up unable to do anything significant in terms of damage” to nuclear facilities that Iran has been moving underground to protect them from airstrikes, Ben-Meir said.

The veteran analyst of Israeli politics said talks between U.S. and Israeli security officials are focused on a possible “insurance policy” for Israel: The United States would provide bombs capable of penetrating and destroying underground facilities. In close consultation with Washington, the bombs could be used against buried Iranian nuclear sites at a later date, allowing Israel to refrain from any military action now that could embroil the U.S. in another war on the eve of the presidential election.

Threats of military action against Iran are spurred by Israel’s frustration with the paltry progress being made at recently resumed negotiations between Iran and six major powers. The talks are aimed at ensuring that Iranian programs are limited to peaceful purposes like energy production and medical research, said Gaukhar Mukhatzhanova, a nonproliferation scholar at the Monterey Institute of International Studies.

“I don’t see any particular breakthroughs in the Iranian program. It’s been on a pretty steady course,” she said, adding that, as far as preemptive air strikes were concerned, “there is technically no urgency to do this.”

Three rounds of high-level talks between Tehran and diplomats from the United States, Russia, China, France, Britain and Germany have failed to produce concessions from either side, and trade sanctions that were tightened last month have succeeded mostly in depriving average Iranians of food and fuel, rather than pushing the regime to open more of its nuclear activities to international inspection.

Still, those pressures are mounting on Iran and raising the cost - both financially and politically - of the regime’s nuclear pursuits, said Alireza Nader, senior policy analyst on Iran for Rand Corp. He pointed to reports of Iranian demonstrations against rising food prices and shortages, along with demands, even from Iranian elites, that the government give priority to social needs over nuclear investments.

“According to the U.S. intelligence community, the Iranian leadership hasn’t even made the decision to weaponize their program,” Nader said. “They’ve been creating the technical know-how and the infrastructure, but they haven’t made that decision, and there is much more time than the Israelis portray there to be. I don’t think an Iranian nuclear weapons capability is inevitable or imminent.”