Menachem Begin paid a heavy price this past week for having sent Israel's armed forces into west Beirut.
The President of the United States in Washington held Prime Minister Begin responsible for the dreadful consequence of that move (the massacre of several hundred Palestinian men, women, and children), demanded the immediate withdrawal of those Israeli forces, and sent US Marines back to Beirut, along with French and Italian troops.
The purpose of the return of the US-European force was to guard Arabs, not to guard Israel against Arabs.
This reversal of the usual US role in the Middle East was only one of many changes in the Mideast pattern which followed swiftly on the news that ''Christian'' Phalangist militia men had been admitted to Palestinian refugee camps by Israeli troops and had committed there a two-day indiscriminate killing , in the words of one survivor, ''of anything that moved.''
The Israeli government denied responsibility for the killing, but in Washington John Hughes, the State Department spokesman, said:
''Israel assumed military control of west Beirut. When you take military control, you assume responsibility for what happens.''
Opinion on Capitol Hill in Washington was affected both by news of the massacre and by the subsequent refusal of Mr. Begin and his Cabinet to authorize an official investigation of the massacre and of the events leading up to it. Even congressmen who normally support Israel in all its actions recognized that this spelled the end of any idea of an increase in the annual US subsidy to Israel.
Israel received $1.3 billion in US military aid and $785 million in economic aid in the 1982 fiscal budget. The Reagan administration had intended a higher figure in the new budget. There will be no higher figure. There might be a cut in the old figure, which is the highest level of aid on a per capita basis that either the US or the Soviet Union gives to any client.
Cuba, with three times the population of Israel, gets roughly the same dollar's worth from Moscow that Israel gets from Washington. Vietnam, with roughly 20 times the population of Israel, gets about half as much from Moscow.
For the first time in the history of Israel many of the most influential American newspapers, magazines, and broadcasting programs were highly critical of Israel's actions. Support was general for President Reagan's plan for a ''new start'' toward peace in the Middle East. That ''new start'' had called for an immediate freeze on Jewish settlements in occupied Arab territory, for withdrawal of Israeli forces from Lebanon, and for prompt negotiations looking toward the establishment of an independent Arab community in the occupied territories of the West Bank and Gaza.
During the week Washington continued talking with the moderate Arab countries , trying to keep them in line for peace negotiations. Washington officials regarded the attitude of the Arab countries as being modestly promising. Washington disagreed openly with the Begin contention that the Arabs had rejected the President's peace proposals.
For the first time there was serious criticism of Israeli policy in the American Jewish community. And in Israel itself there was a vigorous and vehement - although still a minority - opposition to Begin policies. At this writing, one member of the Cabinet had resigned. The architect of the government's ''hard-hand'' policy toward Palestinian Arabs on the West Bank, Menachem Milson, also resigned over Mr. Begin's refusal to have an official investigation of the massacre.
Public opinion in the US had become less supportive of Israel before news of the massacre. An early September Gallup poll showed a drop in the ''favorable'' rating for Israel from a 1981 high of 74 percent down to a new low of 56 percent. The ''unfavorable'' rating went up from 19 percent in 1981 to 36 percent in early September. Polls taken after news of the massacre are expected to show a further decline in US public support for Israel.
As of this writing, Mr. Begin was taking steps to comply with the American President's demand for an Israeli withdrawal from west Beirut. The Israeli Cabinet had, apparently with reluctance, agreed to allow the mixed US, French, and Italian armed force to return to Beirut. But Mr. Begin continued to resist the idea of any full withdrawal from Lebanon, and continued to refuse to put a freeze on Jewish settlements in West Bank and Gaza territory.
The central feature of the whole Mideast situation is that the President of the US and the prime minister of Israel are now pursuing conflicting policies. Mr. Begin is pushing toward Israeli annexation of all of the occupied Arab territories. The American President continues to work consistently for an ultimate peace between Arabs and Israel involving Israeli withdrawal from most of the occupied territories.
There can be little doubt that the facts of the massacre and of the refusal by the Israeli Cabinet to authorize an investigation have weakened and damaged Mr. Begin and his policies inside Israel, in the world generally, with American public opinion, and in the Congress in Washington. Mr. Begin can no longer assume that in a test of strength in Congress he will necessarily win out over the American President.
The other side of the same coin is that the prospect has improved that someday the Arabs of the occupied territories will be able to live under their own laws and their own leaders. The President of the US is publicly committed now to that purpose. Mr. Begin has weakened, not advanced, his own purposes by sending his troops into west Beirut in explicit defiance of the wishes of the American President.
Political observers of the Mideast doubt that opposition to Begin policies in Israel will be sufficient to bring down his government in the visible future. Some polls in Israel seem to show that he has stronger and more widespread backing than ever, although also more vigorous opposition. But he can no longer take American support for granted, or a continuation at rising levels of the most generous subsidy any superpower gives to a client.
James Reston in the New York Times noted this week that the US subsidy comes to ''between $3,500 and $4,000 a year for every family of five in Israel - which is more than the unemployed get in Detroit.''