The American public's support of Israel -- as distinct from some Israeli actions -- remains virtually as strong today as in the months before Israel's invasion of Lebanon and bombing of Beirut, according to a Washington Post-ABC News poll.

Americans nevertheless are sharply critical of the extent of the bombing, but they tend to believe the Israeli actions will result in a change for the better, not the worse, in the Middle East.

At the same time, there is widespread concern that the war in Lebanon has damaged American relations with the oil-producing Arab nations. There is a sharp decline in the number of people who regard Israel as a trusted ally of the United States, and an increase in those who feel that President Reagan is leaning too much in favor of Israel.

In effect, the new poll strongly suggests that many Americans are in a process of reappraising their thoughts about the relationship between the United States and Israel, finding much that is positive -- but much that is negative as well -- in events since the June 6 invasion. One of the poll's most striking findings, however, is the lack of attention from many Americans toward the crisis in the Middle East.

There appear to be two American publics: a minority that is following developments in Lebanon at least fairly closely, and a large majority that has little or no knowledge and interest at all. Frequently the views of the two publics are at sharp variance, with the better informed group holding more pro-Israel views.

Only 36 percent of the 913 people interviewed in the nationwide telephone poll were able to name the two countries -- Egypt and Israel -- that participated in the Camp David peace talks when Jimmy Carter was president. Among them, interest in Lebanon is fairly high, with only 18 percent saying they are not following events there at all closely.

But among the rest, despite more than two months of extensive daily television and newspaper coverage, six in 10 say they have not followed the news in Lebanon at all closely. Only 5 percent of them say they have followed the events since the June 6 invasion very closely.

The divergence in attitudes of these two publics makes interpretation of the "national mood" toward the Middle East extremely complex. For example, those who appear better informed tend to be optimistic about the agreement to remove the Palestine Liberation Organization from Lebanon, and a majority of them favor sending the contingent of 800 Marines to help in the evacuation.

But those who are less informed are pessimistic about the success of the PLO withdrawal, and they strongly oppose the sending of U.S. troops. Such differences recur throughout the poll, and on some of the most important issues.

On one key question -- whether the Israeli invasion of Lebanon was justified or not -- the division is particularly high. By 52 to 38 percent, the more knowledgeable group holds that it was justified. But by 43 to 28 percent, with 29 percent expressing no opinion, the less informed group says the invasion was not justified. For the two groups together, the split is almost even: 41 percent saying it was not justified, 37 percent saying it was.

Overall, when asked, "Are your sympathies more with Israel or more with the Arab nations?" 52 percent of the public choose Israel, and 18 percent choose the Arab nations, almost exactly the split found in a Post-ABC News poll in March, three months before the invasion of Lebanon. But among the more informed group, support for Israel is stronger, with 57 percent siding with Israel.

On one important matter the two groups are in agreement, with virtually no difference in views:

Question: "Would you say the Israeli invasion of Lebanon has helped or hurt the United States in its dealings with the oil producing Arab nations, or what?"

Response: Helped, 10 percent; hurt, 63 percent; made no difference, 11 percent; no opinion, 16 percent.

Conducted by telephone on Tuesday, the poll contained a number of questions that were repeats of ones in the March survey, making it possible to draw comparisons on changes in sentiment brought on by the recent events. Among the highlights are these:

Americans now take a somewhat dimmer view of Menachem Begin, Israel's prime minister.

In March, 39 percent said they had favorable feelings and 22 percent said they had unfavorable feelings toward Begin. The new poll showed 33 percent favorable, 32 percent unfavorable.

In March, Reagan was perceived as leaning more to the Arab nations than to Israel. That sentiment has been reversed, so that among those who think the president is leaning too much in one direction or the other, almost twice as many say he is favoring Israel.

Despite Yasser Arafat's announced intention of winning over American public opinion, there is a stronger sense now than before that his Palestine Liberation Organization does not really represent the views of most Palestinians. In the March survey, 21 percent said they felt the PLO represented a majority of Palestinians and 48 percent felt it did not. In Tuesday's poll, the 21 percent figure remained the same but the number saying the PLO did not stand for most Palestinians climbed to 60 percent.

In the March poll, 54 percent said they regarded Israel as "a reliable ally of the United States--one that can be trusted to cooperate with the United States in almost any circumstances." At that time, 36 percent said Israel was not such an ally. The new poll shows a virtually even split of 44 to 42 on the question.

By a ratio of 2 to 1, citizens said that the heavy Israeli bombing of West Beirut constituted more force than was necessary to force the PLO to leave Lebanon. At the same time, the public supported the overall Israeli goal, with 42 percent saying the removal of the PLO will change things for the better in the Middle East and 22 percent saying it will change things for the worse.