WASHINGTON, Aug 20 (Reuters) - U.S. Secretary of State Hillary Clinton on Friday invited Israeli Prime Minister Benjamin Netanyahu and Palestinian President Mahmoud Abbas to resume direct talks in Washington on Sept. 2 with the aim of reaching a peace deal within one year.

There have been difficulties in the past, there will be difficulties ahead, Clinton said in a statement.

I ask the parties to persevere, to keep moving forward even through difficult times and to continue working to achieve a just and lasting peace in the region.

Clinton's announcement caps months of exhaustive diplomacy by U.S. Middle East peace envoy George Mitchell, who has been shuttling between the two sides in hopes of persuading them to return to negotiations that were broken off in 2008.

The ultimate goal is to establish a viable, democratic and independent state of Palestine existing side by side in peace with Israel.

Clinton said the talks should take place without preconditions and address all of the so-called final status issues, which include the boundaries of a future Palestinian state, Jewish settlements in the West Bank and the status of Jerusalem.

Clinton's statement came as the quartet of Middle East peace mediators -- the United States, Russia, the United Nations and the European Union -- issued its own invitation to both sides to resume talks.

Netanyahu welcomed Clinton's invitation. The Palestinians responded positively to the Quartet statement but had no comment immediate on Clinton's offer, which is the latest U.S. bid to nail down a peace deal that has eluded negotiators for almost two decades.

JORDAN, EGYPT INVITED

Clinton said U.S. President Barack Obama also had invited Jordan's King Abdullah and Egyptian President Hosni Mubarak to attend the Washington summit in view of their critical role in the effort.

She said Obama hoped to hold bilateral meetings with the four leaders on Sept. 1 and that she had invited Netanyahu and Abbas to meet with her on Sept. 2 to mark the formal relaunch of direct negotiations.

As we move forward, it is important that actions by all sides help to advance our effort, not hinder it, Clinton said,

Mitchell said the timing and location of subsequent meetings was being discussed but that some of them could be expected to take place within the region. He said Hamas, the Islamist group that rules the Palestinian territory on the Gaza strip, would have no role in the talks.

Mitchell said the United States stood by its earlier calls on Israel to call a halt to building new Jewish settlements in the occupied West Bank. Israel's self-imposed moratorium on such construction is due to end in late September.

We expect both parties to promote an environment conducive to negotiations, Mitchell said, without indicating whether Netanyahu's government had agreed to extend the building freeze.

He said the United States was prepared to offer its own bridging proposals as necessary during the negotiations but that the process would ultimately be up to Israeli and Palestinian negotiators to thrash out.

We don't expect all of those differences to disappear when talks begin. Indeed, we expect that they will be presented, debated, discussed, and that differences are not going to be resolved immediately, Mitchell said, adding that a final peace deal was in everyone's interest.

Therefore, we are going to continue to pursue that objective with patience, perseverance and determination.