National Security Adviser Stephen J. Hadley will head to the Middle East next week, the latest in a procession of senior U.S. officials trying to keep nascent Israeli-Palestinian talks on track in advance of a possible peace conference later this fall.

The trip was disclosed by officials traveling with Secretary of State Condoleezza Rice, who was in the British capital for talks with Jordan's King Abdullah II after spending four days shuttling between Israel, Egypt and the West Bank.

The United States is working to persuade the Israelis and Palestinians to come together around a common document that would launch negotiations to settle longstanding disputes over such thorny issues as the future of Jerusalem and the borders of a Palestinian state.

A senior State Department official said Hadley will meet with senior Israeli and Palestinian officials in an effort to maintain U.S. engagement at the highest levels.

Rice finished the Middle East portion of her trip by dining with Israeli Prime Minister Ehud Olmert Wednesday night before flying here. She met Abdullah Thursday afternoon, and plans to return to the Middle East in a few weeks, aides said.

Briefing reporters on the plane Thursday morning, Rice said what seemed like a distant proposition only a short time ago--that the two sides could hold negotiations on a final settlement--was now within reach.

"That's encouraging, given all we have been through in the last year," she said, playing down comments by Palestinian leaders questioning Israel's seriousness in negotiations.

"I am not surprised that there are some tensions," she said. "I am not surprised there are some ups and downs. It's the character of this kind of endeavor. But I was encouraged by what I heard."

Rice has steadfastly refused to be drawn into detailing the private talks. But she said she devoted considerable attention during the past few days on how to build confidence between the two sides, especially on security.

She said Israelis are justifiably concerned about the consequences of withdrawing from the West Bank, given the violence that followed their pullback from Lebanon and from Gaza, which was later taken over by Hamas, a group designated by Israel and the United States as a terrorist organization.

"That's a fair question, it really is," Rice said, adding that the parties need to work on addressing how Israel would interact with a new Palestinian state on security.

Officials with Rice said this afternoon that she and King Abdullah had a good discussion about her latest efforts to prepare for a peace conference and the Jordanians are encouraged by those talks in the region.

Rice arrived in London amidst an uproar in Parliament about a surprise 50th birthday party hosted for her nearly three years ago by David Manning, then the British ambassador to the United States.

Under pressure from the Labor Party, the Foreign Office disclosed Tuesday that it spent nearly $10,000 on the soiree -- a figure that did not include a scarlet dress made by Oscar de la Renta, Rice's favorite designer, arranged for in advance so she would have something to change into after she arrived at the ambassador's Washington residence.

The Foreign Office has said its embassy did not pay for the designer gown -- it remains unclear who footed the bill or whether the dress was donated by the designer. Rice's hairdresser was standing by at the party as well, to freshen up her hairdo.

When asked on the plane about the 2004 party, Rice smiled and declined to comment.

Ironically, she will be dining Thursday evening with Manning, as well as U.S. Ambassador Robert Tuttle and former British foreign minister Jack Straw.