By Steve Holland and Matt Spetalnick
WASHINGTON (Reuters) - U.S. President Joe Biden and Israeli Prime Minister Benjamin Netanyahu, uncomfortable allies in the best of times, will put their uneasy relationship to a further test with Israel preparing a possible ground assault on the Palestinian Gaza Strip.
After months of strain over the path forward in the Middle East, the two leaders, who have known each other for decades, have been thrust into a wartime partnership following a deadly, multipronged attack by Hamas militants from Gaza into Israel.
U.S. relations with Israel, Washington’s main Middle East ally, have frayed in recent months with the White House echoing Israeli critics who have organized protests opposing the far-right Netanyahu government’s plan to curb Supreme Court powers.
But the two leaders' differences go much deeper.
As president, Biden has frequently stressed support for independent Israeli and Palestinian states. Administration officials say he has raised it in every conversation with Netanyahu, while asking him to halt the expansion of Jewish settlements in the occupied West Bank.
Having returned to office in late December, Netanyahu opposes Palestinian statehood anytime soon and has approved thousands of new housing units for West Bank settlers.
Their often fraught history includes Biden's time as vice president during Barack Obama’s presidency, when Netanyahu tried unsuccessfully to derail a 2015 U.S.-backed Iran nuclear deal.
Hamas is backed by Iran, Israel's regional arch-foe.
By contrast, Netanyahu had a meeting of minds with Biden's Republican predecessor and potential 2024 opponent, Donald Trump, whose ideological embrace of the right-wing prime minister was accompanied by staunch pro-Israel policies.
Netanyahu has nonetheless hedged and avoided taking sides in the U.S. presidential campaign.
After the weekend Hamas assault - the deadliest incursion since attacks by Egypt and Syria in the Yom Kippur war 50 years ago - Biden set aside differences in multiple phone calls with Netanyahu, saying his team was to give Israel "everything it needs" to fight the militant group, said a senior administration official.
Biden assured Netanyahu of "rock solid" U.S. support, scrambled to bolster Israel's military arsenal and dispatched a carrier strike group closer to Israel in a major show of support.
In his public statements Biden has yet to say Israel should show restraint in its military response or expressed U.S. concern for the Palestinian people, often part of White House reactions during previous crises.
"The president emphasized that there is no justification whatsoever for terrorism, and all countries must stand united in the face of such brutal atrocities," the White House said of Biden’s second call to Netanyahu on Sunday.
WIDER WAR CONCERNS
Biden has directed his team to reach out to counterparts in the Gulf and neighboring countries to try to prevent a spiral into a wider war, especially focused on keeping the Iran-backed Lebanese group Hezbollah from opening a second front on Israel's northern border, administration officials said.
While Biden appears to have given Netanyahu a free hand for now, the policy differences remain and he could change course if the Gaza death toll rises further and the fighting drags on, foreign policy experts predict.
Israeli TV channels said the country's death toll from the Hamas attack had climbed to 900.
In Hamas-controlled Gaza, Israel pressed on with its most intensive retaliatory strikes ever, which have killed more than 500 people since Saturday.
"Eventually, if a conflict drags on for weeks or months, a number of U.S. allies are going to lose patience and publicly call for it to end. At that point, you may see the U.S. back channel to Israel to try and convince Jerusalem to bring the fight to an end," said Jonathan Panikoff, the U.S. government’s former deputy national intelligence officer for the Middle East who is now at the Atlantic Council think tank.
Biden also faces the potential challenge of securing the release of an unknown number of missing Americans who may be held by Hamas as hostages.
At home, Biden faces pressure on his right and his left, with Republican hardliners in Congress accusing him of emboldening Iran with a recent prisoner swap deal, something the president's aides strongly deny.
"If President Biden can stand with Ukraine for as long as it takes, I hope President Biden can stand with Israel for as long as it takes," said Republican Senator Tom Cotton, a foreign policy hawk, on Fox News' "Sunday Morning Futures."
Some fellow Democrats, before the attacks, were asking Biden to scrutinize whether Israel merits the multibillion-dollar military aid package it receives each year, and calling for him to do more for the Palestinians.
The powerful pro-Israel lobby, headed by AIPAC, is a major force in U.S. politics, often backs Netanyahu and is expected to play a role in the 2024 election.
NOT IN LOVE WITH 'BIBI'
Biden, 80, has called himself a "Zionist," and he and Netanyahu, 73, have both spoken of having a long friendship.
But Biden went months without talking to Netanyahu this year. The Israeli leader was unhappy that he did not get a face-to-face meeting with Biden until Sept. 20 and it was not at the White House but in a New York hotel on the sidelines of the U.N. General Assembly.
There, Biden expressed worries about the need for stability in the West Bank and settler violence that increased tensions with Palestinians, a senior administration official said.
They appeared to find some common ground on a U.S. push to broker a landmark agreement to open diplomatic relations between longtime foes Israel and Saudi Arabia. But the Hamas attack delivered a severe blow to that effort, leaving its future uncertain.
Aaron David Miller, a Middle East expert at the Carnegie Endowment for International Peace, said that despite Biden's problems with Netanyahu, "the people of Israel and security of Israel are deeply ingrained in Biden's DNA."
"Biden is not in love with Bibi Netanyahu," he said, using the prime minister's nickname. "But he is in love with the state of Israel, the people of Israel and he'll do everything he can to protect the people of Israel."