In his campaign to justify to the world his two-month-old war against revolutionary Iran, President Saddam Hussein of Iraq has progressively elevated the historic importance of the conflict.

At first, when a quick victory seemed imminent, hussein pictured the war as a highly localized affair with strictly limited aims. When it bogged down in front of Iran's fanatically defended cities, the Iraqi president switched tack, calling the war a struggle of the Arab nation as whole against the "infidel Persians" who have been the Arab's antagonists since antiquity.

When that did not prove strong enough, Hussein took the argument a theological step further by proclaiming the conflict a Moslem holy war, or jihad , to reimpose true Islan on the "herjectic" mullahs who rule Iran.

The real rationale for the war, however, is both simpler and more troubling.

As the 43-year-old president never lets his people forget on the wall-posters they must read and the television propaganda they are bombarded with daily, the war is Hussein's own personal crusade, or in the lexography of the times here, "Saddam's Qadisiya."

Qadisiya, as every Iraqi knows, is the grubby little village in southern Iraq where in the year 635 the Arabs, riding out of Mecca with Koran and sword, first met and defeated the Persians of the Decadent Sassanian empire that had ruled over what today is modern Iraq.

Such a personal identiication with the war is of course a double-edged sword that can cut against Husseins's enemies as well as against himself. By making the war "his war" the Iraqi president has tied his political longevity to the success of his armies in the field.

The Iraqi Army retains an advantage over the still-disorganized and badly led Iranians. But Saddam Hussein is still searching for a "Qadisiya" that would still any internal dissent within the Army or party hierarchy as well as allow him to present himself to the rest of the Arab would as a major political and military leader in the area.

Should the Army falter or the war fail to achieve its stated aims of forcing the Iranians to recognize Iraqi sovereignty over the disputed Shatt-al-Arab water way, then, Western and Arab observers here believe, Hussein would become politically vulnerable -- as a scapegoat put up for sacrifice by rivals and enemies in his own secretive Arab Baath Socialist Party, or by disgruntled Army officers full of frustration at the political decisions that guided them in battle.

"The longer the war drags on," worries one of the best informed Western diplomats in the Iraqi captial, "the more difficult will be Saddam Hussein's position."

Aside from a few minor border posts, in most cases abandoned before the Iraqi advance the Iraqi Army's only real victory so far has been the capture of the commercial port of Khorramshahr on the banks of the Shatt-al-Arab.

The capture of nearby Abadan, site of the Middle East's biggest oil refinery complex, could be the Qadisiya-class victory that Hussein is seeking. But so far its defenders, reinforced with regular Army units and tanks during the siege of Khorramshahr, have proven tenacious and it is considered unlikely that the city will fall any time soon, despite Iraqi claims to have the city surrounded and cut off from any resupply.

That leaves the provincial capital of Ahwaz to the north. But Ahwaz has also proven well-defended and Hussein's main Army, moving from the south with a full armored brigade, motorized infantry, long-range artillery and other accoutrements of war, is still, after seven weeks of inching advance, four miles from the city's southern suburbs. From past experience the real difficult fighting only begins at the city limits behind which the Iranians have chosen to dig in in force.

It is this prospect that, according to diplomatic analysts here, has now led Hussein to organize a major offensive against the small Khuzestan town of Susangerd on the banks of the Kharkeh River. Situated 20 miles from the Iraqi border, Susangered is at a roadhead that leads to Ahwaz, 35 miles to the Southwest. By itself Susangerd is not significant. But its capture, claimed today by the Iraqis an denied by the Iranians after what was probably the biggest battle of the war, would put the Iraqis in a position to try to launch a pincer movement against Ahwaz.

The timing of the battle seems to have been dictated by two factors: the fact that the onset of winter rains is near and will slow if not actually halt any major movements on the Khuzestan plain until the spring and the fact that the 11th summit meeting of Arab Kings an heads of state is scheduled to open in Amman, Jordan, next week.

Hussein, who covets recognition as the major power of the Persian Gulf, would like to enter that conference with his own Qadisiya victory. Not only would it give him the influence he has long sought in the Arab world, but it would also negate any plotting or grumbling by his Baath Party colleagues, many of whom are known to be resentful of the cult of personality he has built around himself and would no doubt be prepared to try to exploit any chinks they might find in his political armor.

A failure to come up with a major victory could in fact provide them with the chink they may be looking for.