The lone Iranian F4 Phantom jet screamed into Iraq, just to the northwest of here, at 70 feet above ground, passing under Iraq's radar screen amid a staccato burst of futile Iraqi antiaircraft fire.

Suddenly, the jet lifted slightly and banked sharply, just as a snaking SAM missile, trailing white smoke, was fired into its trajectory. The Phantom's maneuver beat the missile, which arched into the air, then came crashing down to earth in a shower of sparks, flame and billowing gray smoke.

The jet's successful penetration of the Iraqi defense line 12 miles along the eastern bank of the Shatt-al-Arab waterway today appeared to be one of the few Iranian victories in a war that increasingly seems to be going against Ayatollah Ruhollah Khomeini's Islamic republic.

Here is Shalamche, an Iranian hamlet overrun by the Iraqis in the first hours of their initial four-pronged ground attack against Iran last Tuesday, there is emptiness and disolation.

The village's half dozen buildings are shattered, their sides laid open to the dry, hot winds by gaping shell holes. On the wall of one, there is still an Iranian propaganda poster picturing an American soldier kneeling by the severed head of a Vietnamese with the inscription: "Vietnam disgraced the U.S., the Great Satan."

In front of the building lay the burned-out hulk of an Iranian Army MICV (Mechanized Infantry Combat Vehicle). A second MICV, similarly burned, lay behind a shattered building surrounded by the detritus of war: unexploded grenades and artillery shells, twisted and jagged pieces of shrapnel, the fins of exploded mortars, broken concrete and burned-out wood and scattered old clothes from the residents of the houses nearby.

In a bulldozed pit, there was an ammunition dump full of wooden crates of shells and ammunition. Most of it, like the stacks of BGM71A antitank missiles from the Anniston Army Depot in Alabama, was supplied by the United States during the prerevolutionary days of the shah.

The impressive Iraqi Army that overran Shalamche is deployed on either side of the devastated village as far as the eye can see. Troop transports are tucked away in a date palm grove that separates the dusty, arid plain from the Shatt-al-Arab channel on the Iraqis' right flank.

Heavy artillery pieces, poking out from the trees behind a bulldozed earthen barrier, sporadically belch flames and shake the earth as they fire salvos toward the Iranian lines.

On the left, a long line of tracked self-propelled antiaircraft guns was backed into earthen positions, waiting to try to halt the odd Iranian plane that attempts to blast through them to targets across the border.

On either side of the road to Khorramshahr, tanks and armored personnel carriers are positioned just off the main track, waiting for orders to move into the line.

The confidence of Iraqi troops moving up and down the road past this small, shattered Iranian border post, just nine miles from Iran's besieged cargo port of Khorramshahr, tends to support official claims that the war is going well for Iraq, even if its forces apparently still have not actually captured the port and the still-blazing remains of the vast oil refinery complex at Abadan.

Iranian resistance in Abadan today had weakened to the point that observers across the channel from the inferno, which was once the pride of the Iranian oil industry, could hear only sporadic small-arms fire and none of the outgoing artillery that was still being fired at Iraqi positions yesterday.

Iraq, however, had yet to take Abadan, and for most of the day Iraqi gun positions continued to shell the city and its refinery, whose black smoke covered the sky.

Inside Khorramshahr, Iraqi soldiers were still meeting stiff Iranian resistance. Officers here returning from the city reported that house-to-house combat was going on inside the city.

A line of long-barreled Iraqi 130-milimeter artillery pieces dug in just west of Shalamche kept up a steady and thunderous fire throughout the day at remaining Iranian positions in the Shatt-al-Arab port eight miles south of here.

In midafternoon, one of the Iraqi shells slammed into one of the few undamaged oil storage areas behind the port, sending up a huge column of gray smoke a thousand feet into the air.

Iraqi soldiers moving forward toward the front on mud-camouflaged trucks or returning across the vast dusty plain in captured Iranian Army armored personnel carriers and jeeps appeared relaxed, almost jubilant.

Soldiers smiled at visitors watching their speeding vehicles pass. From tank turrets and truck beds, the Iraqi troops continually flashed their upraised fingers in victory signs.

"There is still fighting going on down there and it is very dangerous," Capt. Abu Rashid, an Iraqi infantryman told a visitor here while guiding him through the ruins of Shalamche. "But tomorrow, or the day after tomorrow, you should be able to go to Muhammara, [the Arabian name for Khorramshahr] with no danger at all."

An Iraqi first lieutenant smiled as he bid goodbye to the visitor. "We are not going to be stopped," he said. We will see you in Tehran."