Senator asks Begin to spare Beirut

Sen. Paul Tsongas (D) of Massachusetts was told by the mayor of Sidon in south Lebanon that confirmed civilian deaths of Lebanese in that city due to the Israeli invasion now total 660, according to an aide traveling with the senator.

The latest casualty figure given by the Israeli military spokesman is 350 to 400 Palestinian and Lebanese civilian deaths in all south Lebanon, including 250 to 300 in the Sidon area.

Arriving in Jerusalem, Senator Tsongas urged Prime Minister Menachem Begin in a private meeting not to send the Israeli Army into west Beirut, although he said he thought the Palestine Liberation Organization should leave Beirut.

Mr. Tsongas told The Christian Science Monitor, ''We talked to Lebanese who supported Israel driving out the PLO, but are now chafing under Israeli occupation. The transition from liberator to occupier is remarkably quick.''

Tsongas said that if a new central Lebanese government was ''perceived to be imposed by Israel, it won't work, it will lack legitimacy. The US,'' he said, ''learned this in Vietnam.''

Tsongas recounted that the prime minister had said the military had advised him that most of the damage in Sidon had been done by the Palestinians. ''I spoke to Lebanese and it is simply not true,'' the senator said, ''and if his military commanders are telling him that, he's got a real problem. . . .''

Tsongas said a solution in Lebanon would require ''bold moves.'' He said, ''(PLO chairman Yasser) Arafat would have to swallow United Nations Resolution 242 and 338; Israel would have to respond with a legitimate West Bank solution; and the United States get involved (which is) the only way to pull it off.''

The senator said he was ''distressed'' over insistence by Mr. Begin that Israel would ''never, under no condition'' deal with Yasser Arafat, even should the PLO leader eventually state clearly his support of Resolutions 242 and 338.