Israeli Ambassador Moshe Arens sent an angry letter to Sen. Charles H. Percy (R-Ill.) yesterday, saying he found it "shocking" that Percy, the chairman of the Senate Foreign Relations Committee, had censored a message from Israeli Prime Minister Menachem Begin. The message was to have been read at a party for U.S. special envoy Philip C. Habib Friday night.

"Although I realize that you may not have agreed with its contents," Arens wrote in the hand-delivered letter, " . . . this glaring omission seems to me to be without precedent."

But the person who actually censored the letter was John Wallach, the foreign editor of Hearst Newspapers who was host of the party at the Corcoran Gallery. He had crossed out seven lines before giving the message to Percy to read. Those lines were interpreted as saying that it was the Israel Defense Forces -- not Habib's diplomacy -- that got the PLO out of Beirut last summer.

"I thought it was insulting to the Arabs to have a message talk about war and terrorism at an evening that was a tribute to Phil Habib and peace," Wallach said in a telephone conversation. Wallach first denied crossing out the lines earlier yesterday, but then called back to change his story--and say that he had shown the Begin message to "several senior administration officials" on Friday, one of whom had told him, he said, that "you can't have him say that."

Percy said yesterday that he agreed with Wallach's decision. "It was not in the best interest of Israel to read that," he said, calling the message "somewhat provocative." But he did read the last sentence of Begin's message, which said: "I join in congratulating Philip Habib on the tribute paid to him."

"It fit in beautifully," Percy said. Asked if he thought it acceptable to edit a solicited message from a foreign leader, Percy said: "Well, I don't know."

The crossed-out lines, as related by Percy yesterday, read like this: "In the wake of Operation Peace for Galilee, Phil Habib made great efforts to bring about the evacuation of the bulk of the terrorists from Beirut and Lebanon. He worked hard to achieve this goal and, with the victory of the Israel Defense Forces, his diplomatic endeavors contributed to the dismantling of that center of international terrorism which had been a danger to all free nations."

Wallach, who has known and written about Habib for years, said he gave the party -- paid for by the Hearst Corp. -- because Habib is an old friend. "There are times when the line between a reporter and the people he covers is less important than the relationship between two human beings," he said Friday.

Arens also wrote a letter to Wallach, saying he was "shocked -- and I was not alone in this feeling -- by the discourtesy shown on this occasion to the state of Israel, its prime minister, and its ambassador."

In the letter, Arens complained of Percy's omission, and also said that the program for the evening expressed thanks to the ambassadors invited -- but left out the Israeli ambassador. (Under the heading of "With Special Thanks To" there appeared 16 ambassadors, including those from Lebanon, Egypt, Jordan, Saudi Arabia, Syria, Oman, Kuwait and Morocco.) Yesterday, Wallach said the Israeli ambassador was omitted because he hadn't responded to the invitation by the time the program was printed.

During the party, which was attended by several hundred people from the diplomatic corps, State Department and the White House, there were messages read to Habib from Ronald Reagan, President Amin Gemayel of Lebanon, King Hussein of Jordan, President Hosni Mubarak of Egypt and former secretaries of state Alexander M. Haig and Henry A. Kissinger. "In none of the many words spoken that evening," Arens wrote to Wallach, "was there a single reference to the only reason that we can discuss at all the prospects for a free and peaceful Lebanon: The Peace for Galilee operations this summer which broke the PLO-Syrian stranglehold on the country. This action cost the lives of over 350 young Israelis."

"I am afraid that the attempt to cater to the ostrich-like attitude of some of the ambassadors from Arab countries who refused to meet or negotiate with Israel or Israelis contributes nothing to peace in the Middle East," Arens continued. "The attempt to ignore Israel and the message from its prime minister seems to me an act of unprecedented discourtesy."

"If that were the case," said Wallach, "I wouldn't have invited the Israelis."