The original scenario had been that Morocco's King Hassan II would do all the talking when he and six others from the Arab delegation met yesterday with President Reagan on the troubling question of peace in the Middle East.

"Hassan worked his crew until 3 a.m. to make sure there was perfect choreography," according to one State Department official. "By the time everybody met with the president, the king apparently felt confident enough about his bull sessions prior to the meeting that he opened it up a bit."

By last night, when Secretary of State George Shultz welcomed Hassan and his party of foreign ministers from Jordan, Saudi Arabia, Syria, Algeria and Tunisia and the secretary general of the Arab League to a black-tie dinner at the State Department, there seemed little doubt that both sides had come away with a feeling of mutual confidence.

"I trust you," Shultz told Hassan as the two of them stood talking in one of the elegantly appointed, antique-filled diplomatic reception rooms atop the State Department.

"His majesty made a number of comments to me yesterday about how things would proceed, and everything that he said came true," Shultz said, turning to a guest.

"It's 20 years of experience," said Hassan.

"Maybe," said the guest,"it's because the king's a total cynic."

The party had been pulled together in less than a week once the powers that be decided the State Department should cap off the first such meeting here by Arab leaders. Among the 150 or so guests were Vice President Bush and several Cabinet officers, including Commerce Secretary Malcolm Baldrige and Energy Secretary James Edwards; Supreme Court Justice Sandra Day O'Connor; perennial office-holder John Connally of Texas; and a host of administration, state and foreign officials.

The "most present absentee," as one Arab delegate put it, was the PLO representative Khalid Hassan, who came to Washington with the delegation but was not received -- either at the White House or, later, at the State Department. Despite his absent presence, the climate surrounding the meetings was what one official called cordial and warm.

When one guest asked if the president understood what the Palestinian problem is, Chedli Klibi, secretary general of the Arab league, nodded his head and said that "now he knows it quite well. He has a secretary of the state who knows the Arab world very well, not only through the briefings he gets but through the involvement in the human situation and the economic and other problems."

After a dinner of filet of salmon, roast pheasant and baked Alaska, Shultz told Hassan that he had been "delighted" when Bush "decided he had to be here." Shultz was so delighted, in fact, that he deferred to Bush in making the toast.

"I firmly believe that today's meeting with the president in the White House will prove to be one of our country's most historic meetings," said Bush. "This search for peace will begin with and be sustained by the free communication of ideas, the will to mold those ideas and the patience to pursue the negotiations and compromises until we can shape a future of security and justice for all. Our meeting here is a key element of that entire process."

In his response, Hassan said it wouldn't be possible to find a solution in a matter of weeks.

"I believe that to achieve peace will be a dfficult course. We will be met by difficulties, but no matter how strong they are they will not be more difficult than the will of peace-loving people. The most important thing is we are about to start those efforts."