Washington - The United States is pushing for a ceasefire in the Gaza Strip that would require Hamas to halt rocket attacks into Israel but would also open crossings into the isolated enclave, US State Department spokesman Sean McCormack said Monday.

Secretary of State Condoleezza Rice spoke to more than a dozen counterparts over the weekend seeking support for the initiative, which would also address tunnels used by Hamas to smuggle weapons from Egypt as part as the three-point approach, McCormack said.

The goal is to create a "sustainable, durable ceasefire" that would bring a lasting end to Hamas rocket attacks into southern Israel, which triggered Israel's military offensive in Gaza 10 days ago.

More than 500 Palestinians have died in the fighting. Israel has rejected international calls for an immediate ceasefire, seeking to cripple the Hamas radical movement so it cannot fire rockets.

President George W Bush said Monday that any ceasefire would have to ensure Hamas does not continue rocket attacks.

"All of us, of course, would like to see ... violence stop, but not at the expense of an agreement that does not prevent the crisis from happening again," Bush said.

Rice spoke with foreign ministers in the Middle East, including Israeli Foreign Minister Tzipi Livni, as well as with her counterparts in Europe. Among them were British Foreign Secretary David Miliband, and the French and German foreign ministers Bernard Kouchner and Frank Walter-Steinmeier.

Rice cancelled a trip to China to remain in Washington and handle the crisis in the Middle East. McCormack said she had no plans to travel to the region.

Israel followed its massive air assault with a ground invasion that began Saturday.

McCormack would not directly comment on the Israeli incursion, saying only "every sovereign state needs to decide for itself how best to defend itself." He again urged Israel to take steps to avoid civilian casualties.

The conflict in Gaza has sparked outrage throughout Arab countries and has further undermined talks between Palestinian President Mahmoud Abbas, whose Fatah party controls the West Bank, and Israel.

Hamas in December declared it would not extend a six-month ceasefire and subsequently stepped up rocket attacks into Israel. The United States regards Hamas as a terrorist organization and refuses to hold any contact with the group.

Hamas forced Abbas' forces out of the Gaza Strip in June 2007 and seized control of the province, dividing the two Palestinian territories.

Meanwhile, Arab countries in New York were seeking a UN Security Council resolution calling for an end to the fighting. The United States has refused to sign onto any resolution that singles out the Israelis as the culprit in the fighting. Arab diplomats were preparing a resolution that could go to a vote as soon as Tuesday.

White House spokeswoman Dana Perino said the Bush administration will work to bring an end to the fighting as quickly as possible, but would not rule out the possibility the situation will spill over to president-elect Barack Obama, who succeeds Bush on January 20.

"We want to get it done as soon as possible," she said. "If we can do that beforehand, that would be something we'd want to achieve."

McCormack said Rice spoke with Senator Hillary Clinton about the crisis on Thursday. Obama has nominated Clinton to become his secretary of state.

Obama, speaking to reporters during a series of congressional meetings, said Monday he was receiving daily briefings on the situation in the Gaza Strip but did not signal whether he would alter the current US policy.

Obama stuck to his position of not commenting on foreign policy before Bush leaves.

"It is particularly important to adhere to the principle of one president at a time, because there are delicate negotiations taking place right now, and we can't have two voices coming out of the United States," Obama said attending a series of meetings with members of Congress.

Obama said he will continue discussions with members of the Bush administration on Gaza developments. Some Arab diplomats have expressed disappointment Obama has not spoken out on the fighting.