* Obama urges Arab world to aid Palestinian's Abbas
* Says Israel has much to gain from seeking peace
By Steve Holland and Alister Bull
UNITED NATIONS, Sept 23 (Reuters) - U.S. President Barack Obama is to make a plea at the United Nations on Thursday for international support for the Middle East peace process, urging world leaders to make sure "this time is different" from previous failed efforts.
Obama is to urge opponents of Israel and the Palestinians to look beyond decades of mistrust and bloodshed and to resist pessimism in support of talks between the parties aimed at creating a Palestinian state living along side Israel in peace and security.
In excerpts of his address to the U.N. General Assembly released by the White House, Obama will specifically urge nations that have pledged support for the Palestinians to meet their obligations for both political and financial support and "must stop trying to tear Israel down."
"Many in this hall count themselves as friends of the Palestinians. But these pledges must now be supported by deeds," he will say, according to excerpts of the speech. Obama is scheduled to speak at 10 a.m. EDT/1400 GMT.
The United States is trying to keep direct talks brokered by Obama between Israel and the Palestinians on track.
But Israel's refusal so far to extend a moratorium on settlements in the occupied West Bank has put the process at risk, with the Palestinians threatening to quit the negotiations if settlement construction resumes when the partial moratorium expires on Sept. 30.
Israeli Prime Minister Benjamin Netanyahu, whose coalition government is dominated by pro-settler parties, has said he will not extend the construction moratorium but could limit the scope of further building in some settlements.
Obama, who brought the two sides together in Washington on Sept. 2 to restart direct talks after a 20-month hiatus, will spell out in his speech that Arab friends of the Palestinians must show Israel how much it has to gain from seeking peace.
"Those who have signed on to the Arab Peace Initiative should seize this opportunity to make it real by describing and demonstrating the normalization that it promises Israel," he will tell the United Nations, while urging Arab nations to offer tangible support to the Palestinian Authority, led by President Mahmoud Abbas.
"Those who speak out for Palestinian self-government should help the Palestinian Authority with political and financial support," he will say.
Obama will also call on all nations with an interest in Middle East peace to get behind the effort and resist "rejectionists on both sides" who will seek to disrupt the process "with bitter words and with bombs."
Middle East peace could be delayed again, he said, "Or, we can say that this time will be different -- that this time we will not let terror, or turbulence, or posturing, or petty politics stand in the way."
The Jewish settlements on the West Bank, which Israel seized during a 1967 war, are deemed by the World Court to be illegal, a finding disputed by Israel. Palestinians fear the enclaves will deny them a viable and contiguous country. (Additional reporting by Arshad Mohammed; Editing by Eric Beech)
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