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By Sue Pleming and Louis Charbonneau

UNITED NATIONS, Jan 8 (Reuters) - The U.N. Security Council called on Thursday for an immediate ceasefire in Gaza that Arab nations hope will put an end to Israel's 13-day offensive, but the United States unexpectedly abstained in the vote.

A resolution crafted in three days of haggling between Western and Arab states "stresses the urgency of and calls for an immediate, durable and fully respected ceasefire, leading to the full withdrawal of Israeli forces from Gaza."

It also called for arrangements in Gaza to prevent arms smuggling to Palestinian militants and reopen border crossings, and for the unimpeded distribution of aid in the territory, where more than 750 Palestinians have been killed.

The United States, which along with Britain and France sought to win over Arab states to the resolution, had been expected to vote for it and its abstention came as a surprise. The 14 other countries on the council voted for the measure.

Some Arab officials feared the U.S. abstention could weaken the pressure on Israel to comply.

Diplomats said Secretary of State Condoleezza Rice, who spoke several times during the day with Israeli Prime Minister Ehud Olmert, talked by telephone with U.S. President George W. Bush just before the vote took place.

Rice told the council Washington backed the resolution and abstained only because it wanted "to see the outcomes of the Egyptian mediation efforts in order to see what this resolution might have been supporting." She was referring to a plan announced this week by Egyptian President Hosni Mubarak.

By not voting for the resolution, the United States was seen as siding with its close ally Israel, which attacked Gaza on Dec. 27 in a bid to stamp out rocket fire by Palestinian militants against southern Israel.

Arab countries, many facing strong anti-Israeli sentiment at home, insisted the Security Council must issue a binding resolution that would force Israel to end its military campaign in the Gaza Strip immediately.

Israel had opposed the idea of a binding U.N. resolution. The Jewish state's U.N. ambassador, Gabriela Shalev, made only a fleeting reference to it in a brief speech to the council that again defended the attack on Gaza as self-defense.

OBJECTIONS DROPPED

The United States had initially backed Israel in opposing a resolution but diplomats said it then dropped its objections and agreed to go along with a cautiously worded text.

Rice, British Foreign Secretary David Miliband and French Foreign Minister Bernard Kouchner extended their stay in New York to negotiate with Arab ministers at the United Nations on a compromise text.

Miliband told the council the resolution, drafted largely by Britain, showed "a genuine consensus on a clear set of objectives" and the United Nations had "served its purpose of speaking loudly and clearly and authoritatively and unequivocally."

Palestinian Foreign Minister Riad al-Malki said, "Israel, the occupying power, must immediately implement this resolution," but later told journalists he feared it would not.

Arab and Western diplomats differed over whether the resolution placed a legal requirement on Israel to end its offensive.

Western countries had originally pushed for a low-profile presidential statement by the Security Council. Arab ministers rejected that as inadequate.

Western diplomats said some Arab governments were keen for a resolution to be passed before Muslim Friday prayers, to deflect potential criticism from preachers.

In the U.N. skyscraper, Arab ministers huddled in basement meeting rooms, while Western powers had their base two floors above them, shuttling back and forth with suggestions.

As agreement neared, a British expert delivered an amended text to Arab ministers while they grabbed late-afternoon sandwiches and coffee in a smoke-filled cafe in the basement.

A Western diplomat said there was something for both Israelis and Palestinians in the final text of the resolution.

"You need to give the Israelis something which responds to their legitimate security concerns about smuggling, and the balancing element of that for the Palestinians is to find a sustainable way of opening the crossings" into Gaza, he said. (Writing by Patrick Worsnip; Editing by Peter Cooney)

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