What good is achieved by the joint Soviet-American statement favoring an early Geneva conference on the Middle East? What harm does the statement do? Those are the questions that have to be asked in assessing the latest turn of events in the Middle East.

The starting point for analysis is the position of the Soviet Union. Having been cold-shouldered by Egypt and Syria, the Russians how hang on in the Arab world by their fingernails. About all they have going for them is the co-chairmanship (with the United States) of the Geneva peace conference, and the possibility of providing military aid to discontented parties, notably the Palestinian Arabs.

In these conditions, the Russians were bound to favor a reconvening of the Geneva conference. While they might talk up the claims of the Palestinians especially loudly and be coy about Israel's right to exist, they were in fact bound to go along with any decision by the Arab states. Thus, in agreeing with Secretary of State Cyrus Vance to move on to Geneva, Foreign Minister Andrei Gromyko gave up nothing.

Unlike the Russians, the United States had a lot to lose. Oppositions to Russia in the Middle East has solidified this country's ties with Israel, with Egypt, and - through the paymaster of the Arab world, Saudi Arabia - with Syria. In consequence the United States alone is in position to promote negotiations between Israelis and Arabs.

Israel has long been willing to deal with the neighboring Arab states - Egypt, Jordan and Syria - returning bits of territory for steps toward peace. The hangup has been the Palestinian Arabs.

They have aspirations for a Palestinian state that the Israelis fear threaten the existence of a Jewish state. They are concentrated in two bits of land - the West Bank of the Jordan and the Gaza strip - which Israel seized in the 1967 war and refuses to abandon. They have various potential leaders ranging from moderate notables on the West Bank to firebreathers in the exile organization, the Palestine Liberation Organization.

The Arab states have insisted that the PLO is the only legitimate spokesman for the Palestinians and that it should be represented at the Geneva conference. They have publicly, at least, favored a Palestinian state based on the West Bank and Gaza, and with some kind of federal links to Jordan or Syria.

The Carter administration has favored the principle of a Palestinian homeland, as distinct from a Palestinian state. It has indicated that the Palestinians, including some members of the PLO, should be represented at Geneva as part of an all-Arab delegation. It has insisted that before the Palestinians participate in a diplomatic process, they accept the existence of Israel as a state.

A delicate compromise linking the Israeli, the Arab and the U.S. positions seemed to be emerging after Foreign Minister Moshe Dayan visited Washington two weeks ago. Dayan indicated Israel would accept Palestinians as part of an all-Arab delegation in a preliminary, non-negotiations phase of a Geneva conference. He said that the Israelis would not admit PLO members, but would not object if the Palestinians leaned toward the PLO.

The joint Soviet-American statement knocks that delicate compromise into a cocked hat. It implied that the United States and Russia were going to impose a Middle Eastern settlement that would begin with PLO representation at Geneva and inevitably end with a Palestinian state.

In Israel the government of Menahem Begin denounced the statement as "unacceptable." Leaders of the Jewish community in this country, who had been won over to Begin largely because of his warm reception by President Carter, called the statement a "betrayal." It was at least possible that the Israelis would refuse to go to Geneva, or that once there they would blow the conference.

Perhaps that ugly scene will not materialize. It is possible that the administration can give assurances that the PLO will accept Israel. It is also possible that the joint Soviet-American statement is part of a larger deal, encompassing progress toward better relations between Moscow and Washington.

But if so, the burden of proof is on the administration. As of now anyway, it is a mystery why the United States agreed with so much fanfare to the joint statement with the Russians. The explanation that comes to mind is that once again, the Carter administration has muddled matters in the Middle East.