If Israeli Ambassador Moshe Arens is telling his leaders what he told reporters the other morning, then the Israeli government is getting a somewhat distorted picture of what the American people think about the Israeli action in Lebanon.
''An overwhelming majority'' of Americans, according to the ambassador, support Israel's move. He said he was referring to polls and that he hadn't seen any polls to the contrary.
A Los Angeles Times poll shows that only about one in four Americans condone Israel's invasion of Lebanon. An NBC News poll shows that a majority of those Americans who say they have heard or read about the Israeli invasion of Lebanon disapprove of it. And a Gallup poll shows that almost as many Americans disapprove as approve of Israel's invasion. Mr. Arens can take no comfort from those surveys.
Further, Mr. Arens told the reporters, in his travels around the United States and talks with Jewish groups he found unprecedented ''solid support'' for the Israeli action.
But this isn't the picture being portrayed by many members of the US Jewish community who, through comments and letters that have been published, are letting it be known that they have great misgivings because of the innocent people who have been injured or killed as a result of Mr. Begin's initiative.
Mr. Arens would only concede that Israel and Prime Minister Begin were doing badly in terms of US public opinion ''in a relative sense.'' And even that loss, he maintained, came as a result of ''a campaign of slander and vilification going on in the United States, of unprecedented proportions.''
The ambassador cited an advertisement published in some US newspapers that was signed by an organization called ''Concerned Americans for Peace.'' He charged that the advertisement contained ''slander and lies'' about Israel's activities in Lebanon. When pressed to disclose who was responsible for the ad, Mr. Arens said: ''We haven't found out yet.''
Mr. Begin doubtless reads the American press. So he could well be making his own judgments about American attitudes toward him and his actions in Lebanon.
But obviously Ambassador Arens is Mr. Begin's man in America, his chief eyes and ears. So the prime minister could be shaping his plans, even toward the next step in Beirut, on advice from Mr. Arens which might (on the basis of his remarks) be along these lines:
''Don't pay too much attention to what you hear about US public criticism of what you are doing. It is not too deep or widespread.''
That's the kind of appraisal that could lead Mr. Begin to what many Americans , including many Jews, would term further recklessness.
What the ambassador should be telling his government - if he wants to provide a truer picture of attitudes in the US - is: The American people are, for the most part, still supportive of Israel on the basic issue of its right to exist as a nation. But there is a widespread perception among many Americans that there has been needless killing and destruction by the Israelis. And there is a comparable widespread adverse feeling, approaching a protest, that US arms have been unlawfully used in these Israeli excesses.
Reporters also find that many Americans are irritated by Mr. Begin's failure to confer with President Reagan on how far he would carry his military initiative and still have the right to use American-supplied arms under the ''self-defense'' limitation imposed by the US. In fact, many Americans see Mr. Begin treating the President, and the US, in quite a cavalier, even insulting, fashion.
This is what Ambassador Arens should be telling Mr. Begin if he wants to put him in a position to deal intelligently with the realities of US attitudes today.