The dilemma of how to oust the Palestine Liberation Organization from Beirut becomes daily more complex for Israel.
Current stategy emphasizes political pressure. But in the background military options are still definitely under consideration.
The longer the negotiations, headed by United States envoy Philip C. Habib, drag on, the more confusing the problem becomes. New factors are arising such as the Iranian invasion of Iraq and US opposition appears to be growing to an Israeli military assault on west Beirut.
At the same time, pressure for military action increases in Israel as the continuing siege of Beirut adds Israeli casualties daily. The siege is begining to take an unpleasant resemblance to the war of attrition with Egypt at the Suez Canal in 1969. That was a type of war Israeli leaders have repeatedly said they will not fight again.
Although Israeli officials voice increasing skepticism that the PLO really intends to leave Beirut, Prime Minister Menachem Begin appears ready to wait long enough to ensure Israel will not be blamed for any diplomatic failure. But apparently, not longer than 30 days, following Mr. Begin's July 17 statement indicating for the first time a limit to Israel's patience.
Israel's initial caution is attributed in good measure to the tone of US President Ronald Reagan's message to Mr. Begin late last week cautioning that a ''military assault'' on west Beirut would ''greviously affect our bilateral relations.''
However, there are other reasons why political pressure is being tried and why the most drastic military options are reportedly being opposed at present by the prime minister as well as many Cabinet ministers. Storming Beirut with attendant massive civilian casualties would risk creating a negative world image for Israel and would rack up large numbers of Israeli casualties that could become a domestic political liability after the war. Dissent at home to the war's conduct is not seen here as a major factor in the prime minister's considerations, though it has roused him to sharp reports and has prompted much painful soul searching in the media.
But, other equally pressing reasons work against Israel's ruling out some form of military option or permitting negotations to drag on indefinitely.
Prime Minister Begin has promised publicly that not one ''terrorist'' will remain in Beirut. If the Israeli Army retreats while PLO men are left in the Lebanese capital this will be represented as a major PLO victory. It will create immense questioning at home, where a recent Jerusalem Post newspaper poll reported that two-thirds of the Israeli public believes the war will remove the PLO threat from Lebanon.
With the expected new emphasis on the Palestinians in George Shultz's State Department, the Israelis are sensitive to PLO maneuvering for formal recognition by the US as the political price for leaving Lebanon.
Jerusalem sources quickly dismissed a statement by leading Palestinian moderate Issam Sartawi last week that the PLO had formally acknowledged Israel's right to exist.
They pointed to an interview by PLO Foreign Minister Farouk Khaddoumi in a Vienna newspaper on July 14 calling for ''coexistence with the Israelis in one state.'' This is a position which Israel considers tantamount to a call for its destruction.