WASHINGTON, Feb 23 (Reuters) - The United States plans to pledge more than $900 million to help rebuild Gaza after Israel's invasion and strengthen the Western-backed Palestinian Authority, a US official said on Monday.

The money will be channeled through UN and other bodies and will not be distributed via the militant group Hamas, which rules Gaza, said the official, who spoke on condition of anonymity as US Secretary of State Hillary Clinton plans to make the announcement next week at a Gaza donors conference in Egypt.

The March 2 donors conference in Egypt's Sharm el-Sheikh resort aims to raise humanitarian and rebuilding funds for Gaza after Israel's invasion at the end of last year, which killed 1,300 Palestinians.

Preliminary estimates put the damage in Hamas-run Gaza after Israel's offensive at nearly $2 billion.

Clinton's bid for funds could face an uphill battle in Congress where requests for Gaza will likely meet resistance as Hamas continues to rule there and the US focus is on its own souring economy.

In December, the former Bush administration said it would give $85 million to the UN agency giving aid to Palestinian refugees in the West Bank, Gaza, Jordan, Lebanon and Syria.

Hamas is labeled a terrorist group by the United States and money must be channeled through UN bodies or the Palestinian Authority run by Western-backed President Mahmoud Abbas.

The United States wants Abbas' PA to play a central role in the reconstruction effort in Gaza, hoping this will increase its influence in the Hamas stronghold. Washington is also putting pressure on other donors to bolster the Palestinian Authority.

We call on donor countries to focus their pledges to meet the Palestinian Authority's priorities, including budget support, and on projects that can be funded through the Palestinian Authority and other existing, trusted mechanisms, said the State Department official.

The quartet of Middle East mediators -- the United States, the European Union, Russia and the United Nations -- are expected to meet on the sidelines of the Egyptian conference where they will work on strategy on Gaza, U.S. officials said.

We will also emphasize the importance of laying the conditions for successful negotiations toward the two-state solution and an end to the Arab-Israeli conflict, a State Department official said of discussions in Sharm el-Sheikh.

Egypt will be Clinton's first stop on a trip expected to include Israel and the occupied West Bank -- a public demonstration of the Obama administration's promise to make Arab-Israeli peacemaking a foreign policy priority.

The State Department has not formally announced her other stops in the region but Israeli officials said Clinton was expected there on March 3 after the Egyptian conference.

Clinton's special envoy to the region, George Mitchell, is set to visit there this week in a bid to revive stalled Palestinian statehood talks complicated both by Hamas and political uncertainty in Israel after the election last week. (Editing by Vicki Allen)