On the rain-soaked flats outside the island city of Abadan, Iraqi and Iranian forces are slugging it out in a daily long-range artillery duel, awaiting the dry season and a widely expected escalation in their eight-month-old war that may determine the fate of the last Iranian stronghold in the vital Shatt-al-Arab waterway.

The sound of heavy guns rolls across the Mesopotamian plains like thunder in an approaching storm, and after awhile the column of smoke rising over the still-buring storage tanks of what was once the Middle East's largest refinery perceptibly thickens and is later joined by two others as Iraqi shells hit their targets.

Occasionally, an Iranian shell thuds against the ground outside the earth-covered Iraqi bunker a mile from the city, where two Western reporters and their escort sit huddled with the lieutenant colonel in command of a detachment of front-line troops, eating pieces of fresh apple and oranges and drinking cold Pepsi Cola.

The talk is of the war, life in the trenches, the fickle politics of the superpowers, and above all about the man Iraqis hold primarily responsible for a war that refuses to end -- the leader of Iran's Islamic revolution, Ayatollah Ruhollah Khomeini.

"Khomeini is a dodger and a liar," remarked the colonel, who seemed in remarkably high spirits given the monotony of the war and the underground existence forced upon him by the Iranian shelling day and night. "We will cut the Iranians' throats. We will hang onto their land until they recognize our rights."

The same official tough line echoes from the commander of the southern front interviewed earlier in the day at his command post hidden in a date palm grove outside Iraqi-occupied Khorramshahr.

"We are not seizing their land, just holding it until they agree to recognize our rights. But if the war lasts longer, there are additional rights."

For three months now, the fighting here in the Middle East's longest war in contemporary times -- over control of the 120-mile-long Shatt-al-Arab linking Ira to the Persian Gulf -- has been bogged down in an uneasy stalemate awaiting the end of winter rains for a new offensive by one side or the other or a breakthrough in so-far fruitless peace efforts.

Unless the Iraqis take Abadan, the war -- from their point of view -- could well have been in vain, because as long as the Iranians remain there, the Iraqis cannot enforce their claim to the Shatt.

Recent saber-rattling statements by President Saddam Hussein, warning that Iraq stands ready to seize more real estate if Tehran persists in its refusal to recognize Iraqi sovereignty over the waterway, have spurred speculation of a major new Iraqi offensive once the rain-drenched battlefield dries out, making it possible for tanks and armored vehicles to go on the move again.

Here around Abadan, where the Shatigan marshes and the Bahamchir River have flooded to form a huge lake separating Iranian and Iraqi lines, this will not be before the end of May at least, according to Iraqi officers here.

Until then, a full-scale Iraqi assault on Abadan would seem unlikely, or at least extremely difficult because of the flooded marshes. Even with the best of conditions, the battle for Abadan, if and when it comes, seems certain to be a horrendous one.

The Iraqis have had to build a network of dikes to prevent the marsh waters from drowning them in their bunkers and another of interlinking raised roads to keep lines open to their advanced positions like this one a little more than a mile outside Abadan.

The Iraqis say they have so far beaten back five counteroffensives here, the last of them Jan. 9-10 when the Iranians sought to break out of shell-battered Abadan and link up with another force coming down the road from Sheik Abdir to the northeast across the flooded Shatigan marshes.

Judging from terse Iraqi war communiques and reports from Western correspondents visiting other sectors, the story elsewhere along the 300-mile front inside Iran's oil heartland of Khuzestan, from Abadan in the south to Kasr i-Shirin in the north, seems to be much the same as here -- daily exchanges of artillery fire and periodic clashes between the two armies as the Iranians try to break out from one or another of the cities the Iraqis have under siege and are pounding daily with artillery and occasionally missiles.

The Iraqis are also on the outskirts of Ahwaz, the provincial capital; have Susangerd, 35 miles to the northwest, surrounded on three sides, and have reached to within 10 miles of Dezful, another major provincial city 75 miles north.

But since the first two months of the war, which began in earnest with an Iraqi three-pronged attack into Khuzestan on Sept. 22, there has been no major Iraqi offensive to seize any of these heavily defended cities.

Another seeming anomaly in this slow-moving war is the scant use of air power by either side. Throughout a day-long tour of the Abadan front, not a single Iraqi or Iranian plane appeared in the sky and only once during a two-week visit in early April did the Iraqis report the use of jets to attack Iranian positions.

The Iranians, for their part, have reported only one major air attack so far this year inside Iraq, on April 4, when eight of their aircraft raided a number of sites including -- to the embarrassment of the Iraqis -- an air base housing their big Soviet-made TU 22 bombers on the far side of the country near the Jordanian border.

The Iraqis, seeking to explain the Iranian penetration 500 miles deep into their country, said the base hit was near the Syrian border and only by refueling at a Syrian field had the Iranians been able to reach it and evade Iraqi defenses.

The strategy of pounding Iranian cities with artillery from a safe distance without mounting a major offensive has kept Iraqi casualties low -- a prime political objective -- while inflicting considerable damage and losses on the Iranians bottled up inside. Iraqi war communiques often say Iranian casualties are 100 or more a day compared to 20 or fewer for the Iraqis.

Western embassies in Baghdad are skeptical of Iraqi figures, particularly when it comes to their own losses, but believe the Iraqi accounts of the fighting come far closer to the truth than the Iranian ones.

Altogether, the Iraqis claimed as of early March to have killed about 20,000 Iranians since the beginning of the war while suffering the loss of only "several thousands" on their side. Western estimates of Iraqi losses vary anywhere from 6,000 to 10,000, a figure still substantially less than the 16,000 casualties Iraq admits were suffered by the Army at the hands of rebellious Kurds in the north during the last year of their war against the central government in 1974-75.

Here in this southern sector of the war front, the Iraqis say they have penetrated 38 miles into Iran, 22 miles beyond the Karoun River, to dominate all the eastern and northern approaches to Abadan. But they have still not crossed the Bahamchir River separating Abadan island from the mainland to close off the last remaining Iranian supply line into the city from Khasroo Abad farther south on the island and providing access to the gulf.

Why the Iraqis did not try to capture Abadan last fall remains unclear but the southern front commander said he was ordered from Baghdad to stop short of taking the last access road into Abadan after he had already crossed onto the island.

As a result, the Iraqis today are not yet in a position to enforce their claim to total sovereignty over the Shatt-al-Arab, and their main commercial port at Basrah, 60 miles up the waterway, is effectively cut off from the gulf by the Iranian presence on Abadan Island.

The answer to this war puzzle probably lies in Khorramshahr, or Muhammar as the Iraqis call it, the one major city taken by the Iraqis in their initial September and October offensive. The city today is a scene of total devastation, with practically every house riddled by bullet and shell holes and thoroughly ransacked.

The only signs of life are stray dogs and cats and Iraqi soldiers who have taken up positions in the rubble. The remaining Arab civilian population was relocated in a small village behind the city, out of range of Iranian artillery.

The Iraqi commander, in his briefing, said it had taken 24 days to clear the city of its estimated 2,500 to 3,000 Iranian defenders, mostly members of Khomeini's Revolutionary Guard.

He refused to give any estimate of Iranian or Iraqi losses, but he said it involved a lot of house-to-house fighting and was a bitterly contested battle for control of the city.

Judging from what happened here, taking Abadan is certain to be far more bloody and costly. Abadan is defended by the equivalent of about one full Iranian division, including a mechanized brigade, plus 4,000 to 5,000 Revolutionary Guards, according to the front commander, a far larger force than the Iraqis faced at Khorramshahr.

The Iranians also apparently have plenty of ammunition, sufficient to entertain themselves taking long-range artillery shots from the other side of the Shatigan marshes at the single French-made armored car carrying this reporter away from the front lines at the end of the day.

Asked whether the Iraqi Army would storm the island city, the Iraqi commander replied, "it is up to the leadership to decide . . . Because of our high morale it is not difficult to do, but it is up to the leadership."

He, like all other officers interviewed, refused to give his name, saying this was standing Iraqi war policy.

Any attempt to take Abadan will be fraught with dangers, not only because of the possible political repercussions of high casualites on Saddam's government but also because the seizure of Abadan, or any of the other cities of Iran's Khuzestan province now under Iraqi siege, including Ahwaz, would likely make a resolution of the war even more difficult than it already is proving.

"Another [Iraqi] offensive would almost certainly harden the Iranian position and taking another city make things even worse," remarked one Western diplomat.

But, noted another, Saddam is almost obliged now to do something.

"If they don't get the peace talks moving, he has made several threats and at some point he's going to have to put up or shut up."

Such, it seems, is the crux of Saddam's dilemma as the war enters its eighth month with no resolution of the dispute even vaguely in sight.