Imagine two runners in a marathon. Neither one can go the full 26-mile distance. But a big victory will go to the runner that lasts longest.

That image provides a useful way to think about the Middle East these days. For it goes beyond the narrow focus of Israel and the Palestinians to include the far more important developments now taking place in Iran, Irag, Syria and the oil states of the Persian Gulf.

One of the runners in this Middle East marathon is an entry from Egypt and Israel. The two countries start from a strong base. Working together, they remove the most dangerous source of conflict in the whole area. Because of Egypt's size, strength and geographic position, moreover, it provides a cover behind which other Arab states -- notably Jordan and the conservative regimes of the Arabian Peninsula -- could settle their differences with Egypt and Israel.

In the two years since President Sadat visited Jerusalem, the Egyptians and Israelis have developed a program for peace with powerful momentum. It is built around the return of Israeli-occupied territory to Egypt over a schedule that has three more years to run. It features growing cooperation between Egyptian and Israeli officials. Witness the ingenious arrangement for a mixed force to supervise the truce that was worked out here in Washington last week.

To be sure, the Palestinians have not yet been engaged in the Israeli-Egyptian peace process. But even without the Palestinians, it can advance a long way toward peace.

Especially compared with the competition. The other runner in the marathon is the rejectionist front formed back in 1977 to counter the Israeli-Egyptian peace process. The front centers on the Palestine Liberation Organization, with its terrorist apparatus, and three radical regimes of the Ayatollah Khomeini in Iran, of Saddam Hussein in Iraq and of Hafez Assad in Syria.

Working together, the PLO and the three radical regimes can exert great influence. They have the support of the Soviet Union and all its clients. They have kept Jordan, as well as Palestinians living on Israeli-occupied territory, aloof from the Egyptian-Israeli peace process. Last spring they exacted from Saudi Arabia and other oil states a pledge to use maximum economic power against the Egyptian connection with Israel.

But since last spring, the rejectionist front has been coming apart. In Iran, submerged minorities at the edges of the shah's old empire are now asserting themselves against the rule of the ayatollah.

The unraveling there has raised the threat of communal strife in neighboring Iraq. A crackdown by Saddam Hussein in Baghdad has poisoned relations with Syria, where religious contention daily rocks Assad's regime. Those divisions inevitably surface in the PLO, which is now hung up between moderates and militants.

Apart from beating on the Palestinian issue, accordingly, the rejectionist front cannot take even the first steps toward peace. Its hold on other Arab states is weakening. The Saudis, for example, are not only supplying more oil to the United States now, but they are also quietly paying for Egyptian purchases of American weapons.

Elaborate stratagems to bring the PLO into the Egyptian-Israeli peace process make little sense at this juncture. The PLO can do nothing to ease the tremors now sweeping by their own force through Iran, Iraq, and Syria.

Neither, given these difficulties, can the PLO unite in a way that permits all Palestinians to settle with Israel. Nor is sweetening the PLO necessary to promote Saudi cooperation with the United States and Egypt. The Saudis are cooperating despite the PLO.

Courting the PLO, on the other hand, costs dealry. It antagonizes Prime Minister Menachem Begin of Israel. Begin then digs in -- as he has recently -- by more raids against PLO bases in Lebanon and by more action to promote Jewish settlement on Israeli-occupied lands west of the Jordan River. That puts off the Palestinians even more and slows down the peace process.

But Begin, a sick man, is not going to rule forever. The prospect of his leaving opens an indent for an Israeli government more open to compromise. At that point, the united States can sensibly move to broaden the scope of the negotiations. But until then the best American strategy, by far, is to afford strong, steady support to the Egyptian-Israeli peace process -- the runner who can go most of the way in the Mideast marathon.