Is a Palestinian civil war already underway? We may only know when looking back on these weeks and months in retrospect.

Some civil wars start on specific dates. The American civil war began on April 12, 1861 when the Confederates bombarded Fort Sumter. The Spanish civil war began on July 17, 1936 when Franco’s forces seized control of Spanish Morocco and declared their intention of marching on Madrid.

But when did the Bosnian civil war begin? And are the Sunni-Shi’ite killings already part of a civil war in Iraq? Countries sometime slip into civil wars gradually, and no one notices the day on which they have passed the point of no return.

The streets of the Palestinian Authority are not yet as bloody as those of Iraq, yet hardly a day has gone by in recent weeks without exchanges of gunfire in them between Hamas and Fatah supporters, many resulting in injury or death. Two days ago, four Palestinians were killed in the Gaza Strip in such an exchange. The time is past when most violent Palestinian deaths in Gaza and the West Bank have been at the hands of the Israeli army. They are now internecine.

Fatah-Hamas warfare threatens to get worse in the days ahead. In addition to the many different Palestinian Authority security forces that Yasser Arafat was notorious for balancing against one another, rival Hamas and Fatah militias now patrol the cities of Gaza and the West Bank. Full-scale clashes between them are only a matter of time.

Anything can trigger them – and if anything doesn’t, Palestinian Authority president and Fatah leader Mahmoud Abbas’s recent ultimatum to Hamas to accept his call for a Palestinian referendum on peace talks with Israel most likely will. On May 27, Mr. Abbas gave the Hamas leadership 10 days to agree to such a referendum, which would ask Palestinians to vote on the so-called “National Reconciliation Document,” a proposal, drawn up by a committee of Palestinian security prisoners in Israeli jails, to recognize Israeli within its 1967 borders in return for a complete Israeli withdrawal to them and Israel’s recognition of the “right to return” of 1948 Palestinian refugees and their descendants. The 10 days ran out last night.

As far as Israel is concerned, the “National Reconciliation Document” is a non-starter. No Israeli government is going to consider withdrawing to the 1967 borders and the “right of return” would essentially means the end of a Jewish state by flooding it with large numbers of Palestinians who would seriously erode if not eliminate Israel’s Jewish majority.

Mr. Abbas, who is a clever man, knew this when he adopted the document. But he did not adopt it with Israel in mind. He adopted it with Europe and the United States in mind, on the one hand, and with Hamas in mind, on the other. In regard to the former, he wished to demonstrate that he was still the boss of the Palestinian Authority and that, as a leader capable of bringing the Palestinians back to the negotiating table, he deserved Western backing. In regard to the latter, his goal was to force it into a showdown that would strengthen his presidency against his Hamas rival Ismail Heniye, who was elected prime minister in the Palestinian elections of last January.

Hamas is ideologically unable to accept recognizing Israel, but it also knows that it would probably lose such a referendum, since most Palestinians realize that the “National Reconciliation Document” will win them points in the international arena without forcing them to give up hope in Israel’s eventual elimination. This had led it to defy the ultimatum and declare the referendum an illegal attempt to run a presidential end-play around its January victory at the polls.

At first glance, the Palestinian president has set a neat trap for Hamas. If it accepts his call ultimatum it loses face; if it doesn’t, it loses popular support.

The only problem is that if the trap goes off, Mr. Abbas may find his own hand caught in it too. What will he do if Hamas actively opposes the referendum? He cannot back down without losing what little power he has left. Yet if he tries to go ahead with the vote, the chances are good that Hamas will oppose it by forcibly impeding the stationing of ballot boxes and the access to them.

This could be the day on which Palestinian civil war officially breaks out. And it could also be the day on which the Gaza Strip and the West Bank go their separate ways.

This is because any Palestinian civil war will actually be two wars, one in the West Bank and one in the Gaza Strip , with no possibility of either side moving forces from one to the other. And while Hamas stands to win this war in Gaza, Fatah is stronger in the West Bank.

We may thus, before too long, have two Palestinian Authorities in place of one, the first with its seat in Ramallah and backed by Egypt, Jordan, and other moderate Arab countries, and the second with its seat in Gaza and backed by Syria, and Iran, and the radical Moslem bloc. In the first, Mr. Abbas’s referendum will be approved. In the second, it will never take place.

Unless, that is, someone in the coming Palestinian showdown backs down, or if some last-minute compromise is found. If it isn’t, Gaza and the West Bank could well split apart. This would make the Israeli-Palestinian conflict a brand-new ball game.

Mr. Halkin is a contributing editor of The New York Sun.