* American influence, credibility eroded in Arab world
* Regional politics make U.S. diplomacy more challenging
* Obama: U.S. 'does not control everything around the world'
By Arshad Mohammed
WASHINGTON, Aug 1 (Reuters) - The U.S failure to secure a firm ceasefire in the Gaza Strip despite two weeks of intense diplomacy reflects new regional dynamics in which the world's most powerful actor has diminished influence and fewer allies.
When Secretary of State John Kerry left Washington on July 21 on a mission to try to halt the latest Israeli-Palestinian war, more than 400 Palestinians had been killed, mostly civilians, along with 20 Israelis, 18 of them soldiers.
Nearly two weeks later, after Kerry's extensive face-to-face diplomacy in Cairo, Jerusalem, Ramallah, Tel Aviv and Paris and scores of telephone calls, the death tolls have tripled, two ceasefires have collapsed and the violence rages.
Israel declared a 72-hour Gaza ceasefire over on Friday within hours of its taking effect, saying that Hamas militants breached the truce soon after it began and apparently captured one Israeli officer while killing two others.
Renewed Israeli shelling killed more than 70 Palestinians and wounded some 220, hospital officials said, and Israeli Prime Minister Benjamin Netanyahu warned Hamas and other militant groups they would "bear the consequences of their actions."
Beyond the animosity of the two sides - neither of which seem close to achieving its aims - Washington's diplomatic challenge has been made more complex by the erosion of its standing in the Middle East.
Other contributing factors include tensions among big Arab players, who see the conflict as a proxy war against Hamas and its Islamist allies, some clumsy U.S. diplomacy, including bad timing, and strains between the United States and Israel.
"There is no question that U.S. influence has diminished" in the Arab world, said Daniel Kurtzer, a former U.S. ambassador to Israel and Egypt now at Princeton University.
U.S. credibility has also been undercut by its reluctance to intervene in Syria's civil war; Kerry's failed push for wider Israeli-Palestinian peace, which collapsed in April; and Iraq's instability despite a decade of massive U.S. intervention.
U.S. nuclear negotiations with Iran have also fanned Arab fears of a rapprochement between Tehran and Washington.
"It doesn't convey a sense that the U.S. has a full grasp of the complexities of the region," Kurtzer said, suggesting that a perception has begun to take hold among some countries in the region that they can defy Washington without paying a price.
In one telling incident, and a remarkable breach of protocol, Kerry and his top aides were briefly searched with metal-detecting equipment as they arrived for a meeting with Egyptian President Abdel Fattah al-Sisi in Cairo on July 22.
In Israel, hostile media reports, apparently fanned by Israeli officials, harshly attacked the U.S. secretary of state as he left the region.
"John Kerry is an ongoing embarrassment, with the characteristics of a snowball. The further he rolls, the greater the embarrassment," centrist columnist Ben Caspit wrote in the Israeli newspaper Ma'ariv.
Several analysts said neither side seemed ready to stop fighting when Kerry began his shuttle diplomacy, suggesting his timing was off. It is now unclear when, or whether, Kerry might return to the region.
U.S. 'DOES NOT CONTROL EVERYTHING'
President Barack Obama defended Kerry on Friday even as he derided the notion that the United States had lost influence or that it can solve every problem.
"Apparently, people have forgotten that America, as the most powerful country on earth, still does not control everything around the world," he told reporters.
"Our diplomatic efforts often take time. They often will see progress and then a step backwards," he added. "That's the nature of world affairs. It's not neat and it's not smooth."
The U.S. task has been made more challenging by the cleavage within the Arab world between Islamist forces such as Hamas and Egypt's Muslim Brotherhood and traditional powers who see them as a direct threat.
Egypt is a case in point. Al-Sisi, who was the country's top military officer, came to power after the Egyptian military toppled Mohamed Mursi, an elected president who emerged from the Muslim Brotherhood, which has deep ties to Hamas.
"The role of Egypt has changed from being a credible intermediary to being seen as virtually a protagonist, with its own interests at stake and inimical (to or at least) at odds with Hamas," said Rob Danin, a former U.S. State Department official now at the Council on Foreign Relations think tank.
As a result, Kerry turned to Qatar and Turkey, both of which have rulers with much deeper sympathy for Hamas, to influence the Palestinian group to embrace a ceasefire.
In Paris last Saturday, Kerry joined the foreign ministers of both countries, as well as those of Britain, France, Germany and Italy, to make a joint call for what was then a 12-hour Israeli ceasefire to be extended. That ceasefire also, ultimately, collapsed.
The tableau of the seven foreign ministers, but no one from the Palestinian Authority or from the traditional Arab powers of Egypt, Saudi Arabia or the Gulf, irked U.S. Gulf allies.
"The optics of it is read by an already skeptical audience in the Gulf and in the Arab World as the reinforcement of their worst fears," said Ghaith al-Omari, executive director of the Washington-based American Task Force on Palestine.
BOTH SIDES DUG IN
The stakes for both sides have increased since Israel began an aerial and sea bombardment of Gaza July 8 to try to stop Hamas rocket fire from the coastal Mediterranean strip and then followed up 10 days later with a limited ground invasion.
The scale of the casualties - more than 1,500 Palestinians have been killed, most of them civilians, as well as 63 Israeli soldiers and three Israeli civilians - makes it harder for each side to disengage without something to show for the bloodshed.
Neither appears near achieving their aims: Hamas seeks an end to the Gaza blockade and Israel is trying to degrade the Palestinian group's military capabilities, including its rockets and tunnels, and deter it from future attacks.
While on Thursday the White House pressed Israel hard to do more to prevent Palestinian civilian casualties, it appeared to temper its stance on Friday following the apparent abduction of an Israeli soldier.
Speaking to reporters, Obama described the U.S. "dilemma."
"On the one hand, Israel has a right to defend itself, and it's got to be able to get at those rockets and those tunnel networks," he said, adding that on the other, because Hamas launches rockets from civilian neighborhoods, innocents get hurt. (Reporting by Arshad Mohammed in Washington; Additional reporting by Crispian Balmer, Jeffrey Heller and Maayan Lubell in Jerusalem, Nidal al-Mughrabi in Gaza, Yasmin Saleh in Cairo and Amena Bakr in Doha; Editing by David Storey and Frances Kerry)