Israeli Prime Minister Shimon Peres said today that Israel and Jordan were "closer . . . than they used to be some weeks ago" in moving toward talks on Middle East peace.

"I don't want to create the impression that we have overcome the difficulties," Peres said at a news conference at the end of a five-day official visit to Britain. "We are very far from it. But important progress has been made over the past month."

Other participants in the peace process, including U.S. Assistant Secretary of State Richard W. Murphy, were believed to be less optimistic. While noting that there had been some small signs of movement, western diplomats said that the United States is particularly skeptical of Peres' professed belief that Jordan's King Hussein is on the verge of jettisoning Palestine Liberation Organization Chairman Yasser Arafat as his partner in a joint delegation to the talks.

Arafat has refused to meet the conditions that Israel and the United States have set before they will participate in talks including the PLO: a rejection of violence, recognition of Israel's right to exist, and acceptance of relevant United Nations resolutions on the subject.

"I think the hope that the PLO will meet the necessary conditions put before them is disappearing," Peres said today. He said that Hussein will make "a formal approach" to Arafat "in the next few days" and implied that if a positive answer was not received, Hussein would look outside the PLO for Palestinian partners.

Diplomats agreed that Hussein feels "stronger" now in relation to Arafat, as the PLO has been accused of involvement in new acts of terrorism and the movement appears increasingly weak and fractured. At the same time, they said, Hussein's recent trip to Syria -- which supports dissident PLO factions -- had provided him some leverage over Arafat.

But diplomats said they still found Peres' scenario unlikely and suggested that the Israeli leader was engaging in a public effort to appear more generally conciliatory on the peace issue to bolster Hussein's confidence. For Hussein to break from the PLO, they said, would require backing from other leading Arab states that he is not likely to get.

Murphy, who made six trips to the Middle East last year before the last effort to arrange the talks faltered, began a new round of contacts last week.

He has met this week with both Peres and Hussein -- each traveling independently in Western Europe -- and was due back in Washington this weekend to report the outcome.

The reason for Murphy's renewed efforts, informed diplomats said, was a "recognition of time passing by" and a desire to see if a new sense of urgency, felt by both Peres and Hussein for separate reasons, promised any significant movement in their positions.

In the fall, Peres is due to be replaced as prime minister by his right-wing coalition partner, Foreign Minister Yitzhak Shamir, whose position on peace talks is much more rigid.

At the same time, a diplomat said, "the legislative clock is ticking on the Jordan arms package." Last fall, the Reagan administration was forced by congressional pressure to withdraw a proposed arms sale to Jordan. The sale is due for reconsideration March 1, and "it will be very serious if Congress again" rejects the deal after "the president has committed himself" to Hussein.