(Adds Rice backing Abbas' state of emergency, details)

By Carol Giacomo, Diplomatic Correspondent

WASHINGTON, June 14 (Reuters) - The United States on Thursday endorsed Palestinian President Mahmoud Abbas' decision to declare a state of emergency and vowed to stand behind Palestinian moderates committed to peace with Israel as their Hamas opponents took control of large parts of the Gaza Strip.

A Hamas victory in factional fighting in Gaza would deal a serious blow to a U.S. push for peace founded on the premise that Abbas, a U.S.-backed moderate, would be capable of reining in militants and Israel would embrace him as a partner.

"President Abbas has exercised his lawful authority as president of the Palestinian Authority and leader of the Palestinian people," Secretary of State Condoleezza Rice said after Abbas declared the state of emergency and dissolved the government.

"We fully support him in his (effort) to try and end this crisis for the Palestinian people," she told reporters as she met the foreign ministers of Estonia, Latvia and Lithuania.

Hamas, an Islamist group that won a parliamentary election last year, is considered a terrorist organization by the United States, the European Union and Israel.

The United States, whose troops are fighting Islamist militants in Iraq and Afghanistan, has led efforts to isolate the Hamas-dominated government, demanding that it renounce violence, recognize Israel's right to exist and abide by existing agreements with the Jewish state.

Amid growing U.S. alarm over the widening violence, Rice earlier telephoned Abbas and underlined U.S. support for him and other Palestinian moderates committed to a negotiated peace with Israel, State Department spokesman Sean McCormack said.

PEACEKEEPERS HARD TO FIND

The Bush administration would consider an international peacekeeping force for Gaza advanced by U.N. Secretary-General Ban Ki-moon but believes that finding effective troops for the job would be difficult, McCormack told a news briefing.

He said the United States, which recently supplied the Lebanese government with ammunition, would review its security assistance program for the Palestinians. The program currently only provides training and nonlethal assistance.

McCormack said the peace efforts of moderates had been "challenged by those individuals in Gaza who have attacked the legitimate security forces of the Palestinian Authority, who have in a premeditated way decided that they are going to try to extinguish the hopes of Palestinian people for their own state."

"Make no mistake about it, that the way to achieve a Palestinian state is via the negotiating table," McCormack said. "It's never going to be achieved via the use of violence, threats, intimidation or terrorism."

McCormack said the United States had not been informed of any details of Ban's proposal for an international force for Gaza but "of course, we would take a look at whatever the secretary-general has to propose."

But he said it would be difficult to find forces that would be ready and effective to undertake the mission.

"This is a source of profound concern," White House spokesman Tony Snow told reporters after Hamas fighters captured one of the last bastions of Fatah forces loyal to Abbas and declared the "liberation" of the Gaza Strip.

The recent fighting brought closer a division between an Islamist-controlled Gaza Strip and a West Bank where Abbas' Fatah faction holds sway. (Additional reporting by Matt Spetalnick and Arshad Mohammed)

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