The under secretary of State for political affairs was playing it close to the vest.

"A historic moment," said David D. Newsom of President Carter's trip to the Mideast, quick to add that "I was not directly involved in the plans. I sort of take charge of crises that are not on the front page."

He excused himself and drifted off in the direction of "old friends," leaving conjecture about the risks or rewards of Carter's journey to others at last night's dinner given by Moroccan Ambassador and Mrs. Ali Bengelloun for their minister of finance, Abdellatif Ghissassi.

"Even if we get a treaty between Egypt and Israel, the hatchet is out for Sadat," said Charles Mayer, a merchant of coal energy with a native fascination for foreign affairs.

"Everybody knows the real problem concerns the Palestinian refugees. But if we're taken seriously," Mayer continued, "Carter can win. The question is how can anyone in the Mideast take us seriously these days?"

Across the "Moroccan Room," a large, comfortable reception room in the Cleveland Park residence where soft cushions and low banquettes invite guests to settle in indefinitely, Sen. Thad Cochran, the only Republican senator in Mississippi history, was settling in for his debut appearance at an embassy dinner party.

"I would expect Carter's trip was not high risk at all," said Cochran, sounding very much like senators sound at embassy parties. "I would expect that he would not have gone unless he could be sure of finalizing some agreement. It was designed to make him appear a peacemaker."

The Bengellouns are supposed to have set the standards for Arab entertaining along Embassy Row, when they were here the first time back in the early 1960s. Things were done, well, lavishly, according to some of the guests.

"Washington had never before experienced the social approach from that part of the world," remembered Paul Rogers, the former Florida congressman who, with the Arthur Gardners -- also there last night -- were among the Bengellouns' favorite guests.

Considerably more restrained now than in the good old days, the Bengellouns apparently are no less ardent party-givers. Last year they entertained 10,000 guests at either dinners or receptions.

Last night it was a modest four tables of 10 dining on squab stuffed with couscous, salmon mousse, endive and meringue glace, the latter made by the hostess.