An incident at a Washington party the other night had in it everything you needed to know to take a bit of cheer from the state of affairs between the Arabs and the Israelis, and to weep a bit, too.

The party had been conceived as a tribute to Philip Habib, President Reagan's Middle East emissary. Win or lose, the salty, savvy unpretentious Habib is everyone's favorite peacemaker -- one trusts he will not get into trouble and be renamed MX. Hosts John and Janet Wallach -- he is Hearst Newspapers foreign editor -- had the bold thought to make it not just a tribute in word but also in deed. There would be music and then statements from people in high places, and representatives of all the countries of the area would be brought together.

The results of Wallach's inspiration started out to be good news for anyone who wonders how far Arabs have moved toward accepting Israelis in the current "post-Lebanon" phase. One can assume everyone knew the Israeli ambassador would be at one of those unavoidably quasi-public Washington affairs where the relatively few guests made close encounters a certainty. Anyway, to the Corcoran came the ambassadors of at least seven Arab nations that do not recognize Israel. One of them became the first Arab envoy in Washington (other than Egypt's) to greet his Israeli colleague, not simply to bolt or to brush by.

Then, too, they sat still and applauded Charles Malik, the Lebanese former president of the General Assembly, who read a letter from President Amin Gemayel saying in part that it was not conceivable for Lebanon to have peace with one country at the cost of maintaining enmity with another. This inconceivable thing is precisely the prescription of, among others, Syria, whose ambassador was not at the party.

The symbolism of Arabs and Israelis expressing together their confidence in a U.S. peace initiative came through nicely. The event had a special meaning for the Israelis, fixed as they are on the notion that the degree and manner of their acceptance by Arabs lie at the heart of the Mideast peace process. In this sense, it was a diplomatic breakthrough of sorts -- certainly a coup for the sponsoring Hearst people -- and a swell party.

Scarcely had the guests moved out to mix, however, than the gossip, more beloved of Washingtonians than the juiciest hors d'oeuvre, began to percolate through the crowd. Many had noticed that the tribute to Habib sent by Israeli Prime Minister Menachem Begin, and read by Senate Foreign Relations Committee Chairman Charles H. Percy, seemed strangely brief. It turned out that host Wallach, so advised by American officials, had decided some of Begin's words were inappropriate for the occasion: in the lost words, Begin gave Habib second billing to the Israeli army for accomplishing the summer evacuation of PLO "terrorists" from Beirut. The Israeli ambassador's complaint about the cut started circulating. It also turned out the ambassador was not on the list of envoys named in the program.

Thus did an evening that had started out casting a certain glow--it was in hopeful anticipation of just such a result, I think, that all of us guests had come -- entered a second, wickedly Washington phase.

Wallach has taken his share of knocks for the outcome. But his idea was brave and touching, and by bringing Israelis and Arabs to a table -- actually, to separate dinner tables identified by national flags -- he managed no small feat.

It was the Arab ambassadors who created the demand for the evening's cut corners-- corners no slighted country's ambassador could conceivably have ignored--by their refusal to countenance the direct contacts with Israelis that are the mark of dignity and the international norm and that Egypt's precedent has made obligatory for all other Arabs seeking peace.

It was Begin who, in his message, added an overtly political twist, one that could not have failed to be taken as offensive by some of his listeners. Surely the occasion permitted, even required, a more conventional tribute to Phil Habib.

The consolation is that Habib has since gone back to work in the area. It never fails to impress me how little the Israelis and Arabs would have to do -- just to be civil, to relax for a moment -- to let American diplomacy get up a little headway. The party, I think, proved the point.