President Reagan has hardened his criticism of Israel and left open the possibility of imposing sanctions should its army move even farther into Beirut.
By making his warnings to the Israelis more public and more explicit, Reagan was attempting to buy time for his negotiator on the scene, Philip Habib.
But the Israelis' forceful move Aug. 3 against Palestinian positions north of Beirut airport and into the main part of west Beirut itself in effect snubbed the President and ignored his earlier warnings. A consensus seems to be developing here that Mr. Reagan will have to take stronger action - or at least threaten stronger action - than he has as of this writing before the Israeli government will take him seriously and halt its military drive.
Pressure was building on the President to do just that from the United Nations and from most of the Arab nations. The Arab League, representing 22 nations, said that Arab states were calling on the United States to support a resolution at the UN Security Council urging an immediate Israeli withdrawal to positions occupied prior to the latest Beirut cease-fire. A vote on such a resolution would amount to a test for President Reagan, who has been a lifelong, staunch supporter of Israel. If the US were even to abstain on such a vote, and not veto the resolution, it would send a signal to the Israelis.
Precisely because the President is such a strong supporter of Israel, some sources here think he has a certain leverage in the current situation. Mr. Reagan considers Israel a strategic asset to the United States, but he is apparently at odds with some of his top advisers on this point. And it is clear that some advisers would prefer to see a tougher policy toward Israel than the President has so far been willing to agree to. In effect, the President serves as a protector of the Israelis within his own administration.
In a statement issued by the White House Aug. 4, some 12 hours after the Israelis launched their latest attack, President Reagan noted that the Israeli drive on Beirut came only a day after he had made it clear, in a meeting with Foreign Minister Yitzhak Shamir, that the US placed great emphasis on the maintenance of a Beirut cease-fire. The President said a cease-fire was necessary to avoid further civilian casualties and to secure the prompt withdrawal of the PLO forces in Beirut.
The President's tersely worded statement followed a total of three hours of White House meetings of his special crisis management group and of the National Security Council.
White House officials said that in a personal message to Israeli Prime Minister Menachem Begin on Aug. 4, President Reagan emphasized the last paragraph of his statement. It said that he had expressed, through governments with direct contact with the PLO, his strong conviction that the PLO must not delay further its withdrawal from Lebanon. But Reagan also stressed to Begin ''the absolute necessity of reestablishing and maintaining a strict cease-fire in place so that this matter can be promptly resolved.''
Israeli officials argued, meanwhile, that their current attack was in response to Palestinian provocations and that it was not the start of an all-out assault. But US Defense Department officials said that one part of the Israeli drive appeared to be aimed at breaking the resistance of some of the toughest fighters of the Palestine Liberation Organization (PLO) - those located north of the Beirut airport in and around the sprawling refugee camp known as Borj al-Barajneh.
''We see this as a preliminary softening up of PLO resistance,'' a Defense Department official said. ''The purpose is to split the PLO, to get them into small pieces which the Israelis can then crush individually.''
The official said that the possibility of withholding American military aid was not likely to have any effect on the Israelis. He said that it would be like a ''sword thrust into the water.''
Other sources agreed that such a move might only have a transitory effect. But staff specialists in the US Congress argued that support for Israel in the Congress had eroded because of the Lebanon invasion. That erosion has not, however, gone so far as to allow Congress to support a cutoff of American aid to Israel, they said.
In the view of some administration specialists, the threat of an aid cutoff at this point would merely harden Prime Minister Begin's position at a time when the US needs his cooperation. One possible sanction would be for the administration to further withhold notification to Congress of its plan to sell Israel an additional 75 F-16 jet fighters valued at $2.7 billion.