* Palestinians loath to provoke sanctions by US Congress
* Steering clear of UN agencies makes blowback less likely
* Largely symbolic move boosts Abbas's popularity at home
By Noah Browning
RAMALLAH, West Bank, April 3 (Reuters) - When Palestinian President Mahmoud Abbas signed onto 15 international conventions on Tuesday, he shocked the U.S. sponsors of troubled Middle East peace talks. But the move was carefully limited to avoid American retaliation.
Abbas's action may have been designed more as a symbolic act of defiance to shore up his tenuous standing among Palestinians frustrated at the diplomatic impasse with Israel over their goal of statehood than a knife in the heart of peacemaking.
As a non-member state in the United Nations, Palestinians can join 63 international agencies and accords. However, by only signing conventions dealing with social and human rights instead of seeking full membership in U.N. bodies, the Palestinians' foreign minister said they would not provoke U.S. sanctions.
"Frankly speaking, I don't expect any consequences coming from the U.S. Congress regarding this step at all," Riad al-Malki told reporters on Wednesday.
"We did not talk about us becoming members of the U.N. specialised agencies in order for the Congress to activate their decision. We are talking about and we are still talking about letters of submission to protocols and conventions, and that's it."
Peace negotiations are near collapse amid mutual accusations of bad faith. In the latest such episode, Abbas inked the 15 conventions in search of more leverage against Israel after it refused to free a batch of Palestinian prisoners under terms of a previous agreement. Israel, in turn, said it would not release those detainees without a Palestinian commitment to continue negotiations beyond an initial end-of-April deadline.
U.S. officials criticised what they called "unhelpful, unilateral actions" by both sides.
Abbas's limited self-rule administration in the Israeli-occupied West Bank is dependent on U.S. support. Around $500 million in annual aid to the cash-strapped Palestinian Authority helps keep its bloated public sector and security forces afloat.
But Congress has repeatedly docked payments as punishment for Palestinian political decisions it disagrees with, including an earlier bid for statehood recognition. A 1990 law also bars U.S. funding to U.N. bodies which recognise a Palestinian state.
The law put the United States in the awkward position of losing its right to vote in the cultural and educational body UNESCO last year after Palestinians acceded to it in 2011.
U.S. Secretary of State John Kerry pleaded with a congressional foreign affairs committee last month to reassess its U.N. divestment policies - a sign of how badly his State Department wishes to avoid diplomatic damage arising from Palestinian moves.
"On the next issue of the U.N. waiver, please, I've got to tell you, this is a very one-sided event against us...whether or not the United States loses its vote and gets punished for (Abbas) going (to U.N. agencies) is irrelevant to him. He'll go, because it's a tool for him to be able to do things he hopes that, you know, make life miserable for Israel," Kerry said.
"They'll go again if they think it's in their best interests. And who will pay the price? The United States of America. We won't be able to vote."
Palestinians seek an independent state in Gaza, the West Bank and East Jerusalem - lands captured by Israel in a 1967 war. While all parties say negotiations are the best path to peace, Palestinians say they may eventually resort to international bodies to force the militarily vastly more powerful Israel to make concessions for peace.
The U.N. General Assembly voted to recognise Palestine as a non-member state in 2012, entitling them to join the accords which Abbas signed up on Tuesday, including conventions against discrimination against women and for the rights of disabled people as well as the Geneva Conventions.
They burden the Palestinians with few binding commitments on their government, which has been accused of corruption and abuses of detainees and journalists.
Nor do they court retaliation by immediately empowering them to lodge legal complaints against Israel or rattle U.S. foreign policy, a senior U.N. official told Reuters.
"The nuclear option for Abbas would be to go for the International Criminal Court and International Atomic Energy Agency. Those are the ones that matter," the official said.
"(The latest signing is) actually quite a clever move. Abbas is saying that the Palestinians want to be part of the global community and improve its state building mechanisms by signing up to a load of well-meaning conventions. He can turn around and say, 'Why should Israel feel threatened by us signing a convention protecting women's rights?'"
Peace moves by Abbas, a veteran negotiator who has chosen diplomacy over the violent militancy espoused by his predecessors and Palestinian rivals such as the Islamist Hamas, which controls Gaza, have not been welcomed by his countrymen.
Campaigns for recognition at the United Nations, while mostly symbolic, have been praised by many Palestinians.
The 78-year old president - who saw his term expire over five years ago but remains in office because of a stalemate with Hamas over conditions for the next elections - may have been keen to shore up his appeal after Israel over the weekend failed to free a fourth and final group of over two dozen Palestinian prisoners as part of a pledge to restart peace talks last year.
"That's when he reached his endpoint and said, 'I've got to do another measure that's going to improve my popularity,' and going to the U.N. has so far been successful in terms of boosting his popularity," said Diana Buttu, a former legal adviser to Palestinian peace negotiators.
"But as a measure, it's a weak one. He didn't go all the way to hold Israel accountable and he didn't abandon negotiations."
(Additional reporting by Crispian Balmer in Jerusalem, editing by Mark Heinrich)