Jordan and the Palestine Liberation Organization, dropping expressions of bitterness over differences that have marked their relations in recent weeks, appear to have agreed to continue as partners in the Middle East peace process. But Jordanian officials remained silent today about what price, if any, the PLO agreed to pay to maintain the alliance.

The Jordanian government, which in recent days has made its unhappiness with the PLO abundantly clear, limited itself today to a statement that said its two days of talks with PLO Chairman Yasser Arafat were "amicable and brotherly." Arafat and his aides, however, gave no sign of having shifted attitudes toward Israel.

The apparent reconciliation of the PLO and Jordan could present serious obstacles on the road to the kind of settlement envisioned by the Reagan administration and Israeli Prime Minister Shimon Peres.

The talks here with Arafat followed consultations by Jordan's King Hussein with his closest allies in the Arab world, Egyptian President Hosni Mubarak and Iraqi President Saddam Hussein. But they have produced no announcement that can be embraced by Peres, who had hoped to deal with Jordan alone.

Instead, a confident Arafat told a press conference this morning that he still held the key numbers in the equation necessary for a settlement. Hussein and his aides have said consistently that they must have Palestinian participation to move toward peace. Arafat and his supporters have said there will be no Palestinian participation without the PLO.

Despite angry talk about the recent behavior of Arafat and his supporters in the past month, including the killing of three Israelis in Cyprus, the hijacking of an Italian cruise ship and a last-minute cancellation by British officials of a meeting with PLO aides, the Jordanians appear to have found no alternatives.

Arafat, speaking today of the U.S. and Israeli efforts to exclude the PLO from the process, said with an air of assurance, "There will not be peace or stability in the area if they decide to sidestep the PLO."

"If they were able to achieve peace without us," Arafat said, "they wouldn't have hesitated."

In response to a question from an Arab reporter for an Abu Dhabi newspaper, Arafat answered with an Arabic expression that translates roughly: If they don't like it, they can go fly a kite.

Accusing Washington of siding with Israel in a war against the Arab world, Arafat said, "They can sell their qualifications to somebody else, but I won't buy."

After Arafat and a top-level PLO delegation met for a second day of talks with Jordanian officials, including Prime Minister Zeid Rifai, the Jordanian statement also described the "brotherly" atmosphere as marked by "frankness and clarity out of concern for the Jordanian-PLO accord" signed in February.

Jordanian officials and western diplomats had suggested earlier in the week that a PLO badly weakened by recent events would have to face a hard bargain here: either renounce violence and acknowledge Israel's right to exist, or deal with the possibility that it could be expelled from the last country neighboring Israel where it still maintains a substantial presence.

But after a meeting between Arafat and Hussein last night, both sides said that the question of the PLO's explicitly endorsing U.N. Security Council Resolutions 242 and 338, which imply recognition of Israel, was never discused in detail.

Neither was there any hint from Arafat or his colleagues today that they were ready to forego what they call the "armed struggle" and what Israel defines as "terrorism."

In the February accord, Arafat agreed to work for a peaceful solution and said he accepted all U.N. Security Council as well as General Assembly resolutions relating to the Palestinian issue. These recognize the PLO as the representative of the Palestinian people and call for the establishment of a Palestinian homeland.

Today, when pressed about 242 and 338 at the press conference, Arafat reiterated this point. "You can't say 'I want a piece of the cake,' " he told American reporters. It is the whole batch, or nothing, he suggested.

Salah Khalaf, known as one of the most hard-line members of the PLO leadership and an opponent of the current process, said this afternoon that he had come to Jordan expecting a fight with Hussein.

"I had prepared myself for some very tough talks," Khalaf said in an interview. "But they weren't."

There was no immediate response from Jordanian officials to inquiries about whether or why they backed off from the demands they were expected to make.

But Khalaf and other Palestinians here suggested that Hussein may see little reason to press what are considered "American demands" at a time when the U.S. Senate has forced the postponement of a major arms deal that Hussein viewed as an important expression of good will from Washington.

Coming at a time when both the Reagan administration and Peres appear to be pushing forward enthusiastically with efforts to strike a Jordanian-Israeli peace, the seeming Jordanian-PLO reconciliation may now present a serious stumbling block. Mubarak: Excluding PLO Would Be a Mistake ------United Press International

CAIRO, Oct. 29 -- President Hosni Mubarak said today the exclusion of the Palestine Liberation Organization from Middle East peace efforts would be a mistake that would lead to more violence.

Mubarak, talking to reporters, described Yasser Arafat as the "best qualified man" to participate in peace efforts, saying, "We should make full use of him." He added,"I am not taking the side of Arafat for Arafat; I am taking the side of peace."