UNITED NATIONS, June 8 (Reuters) - Under President Barack Obama, the United States no longer provides Israel with automatic support at the United Nations where the Jewish state faces a constant barrage of criticism and condemnation.

The subtle but noticeable shift in the US approach to its Middle East ally comes amid what some analysts describe as one of the most serious crises in US-Israeli relations in years.

Under Obama, the United States seeks to reclaim its role as an impartial Middle East peace broker which critics say it lost during the previous administration of George W. Bush.

Israel became used to unconditional support of the United States during eight years of the Bush administration, said Marina Ottaway, director of the Middle East Program at the Carnegie Endowment for International Peace in Washington.

She said Bush's extreme position makes even mild criticism appear dramatic to Israeli Prime Minister Benjamin Netanyahu and his cabinet.

However, Washington continues to block what it sees as efforts to use the United Nations as a forum for bashing Israel -- which one US official told Reuters was nine out of 10 initiatives regarding Israel in New York.

Obama has also pushed hard to get a fourth round of UN Security Council sanctions against Tehran over its nuclear program, which Israel sees as its top security threats. A vote on new Iran sanctions is expected this week.

There have been slight changes (in US-Israeli ties), but they've caused a disproportionate reaction on the part of Israel, said Ottaway. We haven't seen any drastic changes.

Last week the United States backed a Security Council statement on Israel's commando raid on an aid flotilla that tried to break Israel's blockade of the Gaza Strip. Nine people on one of the ships were killed in the action.

The statement regretted the loss of life and demanded a prompt, impartial, credible and transparent investigation conforming to international standards.

Washington, UN diplomats and US officials said, worked hard to dilute the text so the 15-nation council did not call for an independent investigation and to ensure it did not explicitly criticize Israel.

UNITED NATIONS LYNCH MOB?

Israel was still unhappy with the statement and its supporters accused Obama of abandoning the Jewish state.

In an article called Joining the jackals, Elliott Abrams, who advised two Republican administrations and is now at the Council on Foreign Relations, accused Obama of exposing Israel to a virtual UN lynch mob.

The White House did not wish to stand with Israel against this mob because it does not have a policy of solidarity with Israel, Abrams said. Rather, its policy is one of distancing and pressure.

Abrams also criticized the White House over the recent five-year review conference of signatories to the 1970 nuclear Non-Proliferation Treaty (NPT) that Israel, like nuclear-armed Pakistan and India, has never signed.

Washington backed a call for a 2012 meeting of all countries in the Middle East to discuss making the region a zone free of nuclear and other weapons of mass destruction -- a plan originally proposed by Egypt with Arab backing to add pressure on Israel to give up its nuclear weapons.

After allowing it to pass, the U.S. delegation criticized the NPT final declaration for singling out Israel, which neither confirms nor denies having atomic weapons.

This statement did not satisfy commentators like Abrams, who said Obama had abandoned Israel in the U.N. and in the NPT conference in the course of one week.

Some analysts say Washington wants to improve ties with Arab nations and regain lost status as a neutral peace arbiter while being careful not to alienate pro-Israel voters.

During the George W. Bush years, Washington's automatic siding with Israel on any issue seriously eroded what had been America's long-standing posture as an honest broker in the Middle East, said Mark Fitzpatrick of the International Institute for Strategic Studies in London.

Obama has been trying to reclaim that status, while keeping in mind the domestic political need of not being seen as anti-Israel, he said.

Outside the United Nations, analysts say Obama tried to ease strains with Netanyahu after tensions spiked earlier this year over Jewish settlement construction on occupied Palestinian land.

He coaxed Israel into indirect talks with the Palestinians, his biggest tangible achievement in Middle East diplomacy.

But an Israeli official, speaking on condition of anonymity, said the jury is still out on the Obama administration's approach to the Jewish state.

It's still difficult to decipher the intentions behind the changing US policy at the United Nations, and not just in regard to the Middle East, the official said.

If the Americans are convinced that, through adopting a softer approach ... they will achieve support from countries that heretofore opposed their policy -- they will discover that they are wrong, the official added. (Additional reporting by Matt Spetalnick in Washington and Dan Williams in Jerusalem; editing by Alan Elsner)