Secretary of State John Kerry shakes hands with Saudi Foreign Minister Adel al-Jubeir in Paris, France on May 8. Senior officials from several Persian Gulf nations want a firmer and more specific U.S. promise to protect them from external threats. (Andrew Harnik/AP)

Persian Gulf leaders, set to convene at a Camp David summit this week, are pressing President Obama to strengthen the U.S. security relationship with the region and expand military assurances to address their growing concerns about Iran, U.S. and regional officials said.

Senior officials from several gulf nations said they understand that a mutual defense alliance, similar to NATO, is not possible. At the very least, however, they want a firmer and more specific U.S. promise to protect them from external threats.

“In the past we have survived with a gentlemen’s agreement with the United States about security,” said Yousef al-Otaiba, ambassador to Washington for the United Arab Emirates, one of the six Gulf Cooperation Council countries participating in the summit. “Today, we need something in writing. We need something institutionalized.”

Other officials were less specific. “I don’t have a problem with written or non-written,” Saudi Arabia’s foreign minister, Adel al-Jubeir, said Monday. “Our faith in America’s word is total.”

Obama announced plans for the summit last month, on the same day that world powers struck a tentative nuclear deal with Iran. Persian Gulf leaders are worried that the potential agreement with Iran, which must be finalized by June 30, signals a shift of U.S. alliances in the region.

The Iran negotiations have focused attention on both sides in the close but often uneasy relationship between the United States and the Arab monarchies of the GCC, whose members include Kuwait, Bahrain, Qatar and Oman in addition to Saudi ­Arabia and the UAE.

There are more than 35,000 U.S. service members stationed in the gulf, with major air and naval bases serving as the headquarters for U.S. military operations throughout the region.

The United States first expressed its willingness to use power to defend strategic partners in the gulf against external threats decades ago. Obama repeated that commitment in a 2013 speech to the U.N. General Assembly.

But there has always been “the question of what’s an ‘external threat,’ ” said Philip Gordon, who until last month served as senior Middle East director at the National Security Council. “Nobody can say exactly what it means. That’s the problem with it.”

Although the GCC and the United States have long cooperated on counterterrorism and other threats in the region, including the current U.S.-led air campaign in Syria against the Islamic State, priorities and goals sometimes differ between them, as well as among the gulf states themselves.

Beyond their concerns about Iran’s nuclear program, Sunni leaders in the gulf and elsewhere in the Middle East see Shiite Iran as a hegemonic power bent on expanding its regional influence with arms, money and in some instances even troops, in Iraq, Syria, Lebanon, Yemen and elsewhere. Iran’s power and activities, they believe, would be enhanced with the rapid influx of cash it would receive once sanctions are lifted as part of a final nuclear deal.

The administration shares that concern but thinks that countering the nuclear threat should be the first priority. If a deal can be finalized, the administration believes, it may become easier to address regional concerns with Iran.

While all share a concern about the Islamic State and other terrorist groups, the gulf countries and others in the Middle East would like the United States to pay more attention to ousting the Iranian-backed Syrian government than to terrorist groups.

For its part, the administration wants the gulf partners to work more closely together to integrate the various components of missile defense systems they have purchased, or plan to purchase, from the United States.

At a White House dinner Wednesday, and all-day talks at Camp David on Thursday, leaders will be discussing “what we can do together,” deputy national security adviser Ben Rhodes said in a conference call with reporters Monday. “We’ll be discussing U.S. policies and our approaches, but also GCC policies and approaches, and how we can align those policies on areas of mutual interest.”

“We anticipate some form of statement emerging that reflects the common positions of the United States and the GCC on a range of issues,” Rhodes said.

Initial hopes by at least some of the gulf countries for a mutual defense treaty with the United States appear to have faded. Even if the administration backed such a proposal, a treaty would have to be submitted to the Senate, where concerns about Israeli security would make passage all but impossible.

More modest outcomes are likely to include measures to ease arms sales between the United States and the gulf states, as well as additional joint military exercises. The partners also hope to set up working groups to address cybersecurity, terrorist use of ­social media and other issues.

The buildup to the summit was dominated by an announcement over the weekend that Saudi ­Arabia’s King Salman, whose country is the most powerful in the GCC, would not attend the forum, just days after his government confirmed he would be there.

Both the administration and the Saudis went out of their way Monday to insist that no snub was intended and that the Saudi delegation would be headed by the senior officials most involved in the issues under discussion — the interior minister, Crown Prince Mohammed bin Nayef, and the defense minister, Deputy Crown Prince Mohammed bin Salman.

The White House said that Obama also spoke by telephone Monday with Salman, whose presence in Riyadh was said to be required by the situation in Yemen, where the Saudis have scheduled a five-day cease-fire in their air campaign against Iran-backed rebel forces.

The very fact that gulf leaders are “going to have hours to tell the president how big a threat Iran is” could help ease tensions between the two sides, Gordon said.

It is less clear how they can reconcile not only their competing vision of security threats in the region but also how best to tackle the ones about which they agree. Obama has emphasized throughout his second term that America’s partners overseas need to take more responsibility for managing threats in their own regions.

At the same time, however, U.S. officials have been unsettled by some of the ways they have done so, including the Saudi air campaign in Yemen and increased support for rebels in Syria who are allied with militant groups.

“This is a real tension I don’t think we’ve resolved,” said ­Frederic Wehrey of the Carnegie Endowment for International Peace. “We need to have these gulf states step up to the plate, but we need to do it in a way that we haven’t totally abandoned the reins.”

For their part, the gulf leaders have a “sort of amorphous sense they want to make sure the United States will be with them,” Robert Malley, the current NSC senior Middle East director, said in the Monday conference call.

The leaders have heard “all these stories about the U.S. pivoting and being fatigued” with Middle East wars, Malley said. “They just want to hear that we’re there, that we care.”