The massacre of Palestinian refugees that occurred during the Israeli occupation of west Beirut caused a significant drop in American public sympathy for Israel, according to a poll commissioned by an Arab studies institute.
The poll also indicates that sympathy for the Palestinians has increased even as sympathy for Israel has decreased. But the increased sympathy for the Palestinians and their need for a homeland does not seem to translate into support for the Palestine Liberation Organization (PLO), which has long had a negative image in the eyes of a majority of Americans.
Analysts in the US State Department and in Congress say the poll's findings seemed to reflect American reaction to the Israeli move into west Beirut and, most important, to the massacre of Palestinians at the hands of Lebanese militiamen Sept. 18. But these experts say it is not clear whether the shift in American attitudes is transitory or whether it is part of a more lasting trend.
''There has been no shift in favor of the PLO,'' says a key Senate aide. ''What you have is a greater sensitivity to the Palestinian problem and to the need to deal with it.''
Senate sources say they expect, despite the shift in public opinion against Israel, that Congress during the forthcoming ''lame duck'' session will approve more than $400 million in aid increases for Israel proposed by the Reagan administration for fiscal year 1983. However, one congressional specialist says he doubts that Congress will add anything to the administration-proposed increases and that this would indicate Congress's willingness to exercise greater caution vis-a-vis aid to Israel.
The poll was conducted Oct. 6-11 through telephone interviews with 1,020 American adults representing a demographic cross section of American society. Polling was done by Decision/Making/Information, a US national research institute whose president is White House pollster Richard B. Wirthlin. According to DMI, Mr. Wirthlin himself was not involved.
The poll was commissioned by the Institute of Arab Studies, Inc., in Belmont, Mass. The institute is a non-profit research organization whose board of directors consists mostly of Arab-American academics. Muhammad Hallaj, director of the Institute, says members felt that until recently American pollsters ignored the Palestinian dimension of the Arab-Isdraeli conflict, that American public opinion has shifted, and that a greater depth of polling on the Palestinian issue was needed. The survey dealt as well with attitudes toward Israel, the press, and Reagan administration policy.
Key findings of the new poll included the following:
* Seventy-six percent of those surveyed agreed that based on the US-supported partition proposal of 1947 for both a Palestinian and an Israeli state, the Palestinians should have the right to establish a state of their own.
* Only 29 percent felt that such a state would pose a security threat to Israel.
* Eighty-three percent favored a Palestinian representation at peace negotiations.
* Fifty-five percent opposed a US government move to recognize the PLO as the official representative of the Palestinian people.
Respondents were asked, ''Thinking back a year ago, were your sympathies more with Israelis . . . or the Palestinians?'' A year ago, 59 percent sympathized with Israel, compared with 39 percent today, while 13 percent sympathized with the Palestinians a year ago, compared with 23 percent today.
In response to questions dealing with President Reagan's Sept. 1 Middle East peace plan, 72 percent agreed there should be a freeze on further Israeli settlements on the Israeli-occupied west Bank of the Jordan River. Fifty-six percent agreed that the Israelis shouldn't annex the territories they currently occupy. Sixty percent favored the withdrawal of the Israelis from the West Bank and Gaza. Sixty-nine percent disapproved the Israeli invasion of Lebanon.
Fifty-three percent of the respondents agreed with the statement that the massacre of Palestinians ''would not have taken place if the Israelis would have kept their commitment to the US not to move troops into west Beirut.''
But when respondents were asked: ''Do you think it has gotten to the point where the United States should take disciplinary measures against Israel because of its invasion of Lebanon?'' only 35 percent agreed. A total of 57 percent opposed such disciplinary action.