The air-raid sirens started screeching like a banshee through the dusty streets of this ramshackle port city today but, after four days of air raids, its remaining inhabitants hardly seemed to mind.

To be sure, a few cars rushing down the main boulevard braked sharply and turned down narrow side streets. And out by the port to the north, on the contested Shatt-al-Arab, antiaircraft units put up a sporadic cover of flak and tracers that sparkled against the black column of oil smoke boiling out of the nearby petroleum tank farm, bombed two days ago.

But a lone bus in the city center did not even slow down, moving along its usual route, spewing diesel fumes over the potholed streets. Half a dozen taxis followed suit, ignoring the rattle of antiaircraft guns and the pop-pop of exploding flak.

Pedestrians looked up at the sound of the siren, with a sort of cold calculation that comes with even the most limited experience of war, then continued along their way convinced that, this time at least, Iranian F4 Phantoms that have devastated many of the surrounding oil installations, and part of the city center as well, were not raiding again.

That was at 5:39 p.m. -- just the latest of a series of air raids through this day, the fourth of full-scale war between the two neighboring OPEC nations of Iraq and Iran. Before dark fell an hour later and the city was plunged into an all-night blackout, there were two more air raid warnings with the same pyrotechnics in the sky.

During the last raid warning, at 6:30 p.m., there was a phosphorescent flash at ground level to the east, out over the Shatt-al-Arab. Radio Baghdad later broadcast that an Iranian jet had been downed, but to the visitor mired in this semi-deserted city in southern Iraq it was impossible to verify.

That war has taken its toll in and around this port -- which before the fighting had an estimated population of 200,000 -- a fifth of whom were technicians from America, Europe, South Asia and Japan -- was obvious.

Miles before arriving in the city the evidence of recent devastation of Iraq's petroleum-based economy assaults the eye with huge, spiraling columns of smoke that rise up from bomber-out refineries and petrochemical plants.

Looking at the tall columns of smoke rising out of the vast refinery at Shuaiba, west of Basra, or from the tank farm at Sharika Muftir, between the city center and the Shatt-al-Arab, one is struck more by signs of smaller refineries and industries that are still standing, almost deserted but relatively intact after four days of air raids.

South of the city towards the border with Kuwait, a small refinery stands unharmed. Even at Zubair, site of the Basra petrochemical complex No. 1, one of Iraq's showcase industrial developments which was bombed Tuesday morning, the main industral complex is undamaged, although several workshops and residential areas have been devastated by bombs and fire.

In the city itself, the streets are relatively empty. Most of the city's foreign community has fled and many Irqis, especially women and children, are gone as well.

There are none of the usual military roadblocks that spring up like mushrooms in similar conflicts. But every block is patrolled by reserves, a sort of Home Guard of youths and paunchy middle-aged men in khakis armed with AK47 assault rifles. These they turn to the sky at every hint of an approaching plane and fire futilely at aerial ghosts that are rarely seen, much less hit.

If the air war is still a daily occurrence, the other war, on the ground and on the water, has moved away now. Those parts of Iran directly across the Shatt-al-Arab, that vast navigable confluence of the Euphrates and Tigris rivers which leads into the Persian Gulf, are quiet.

Apparently they have already been conquered by an Iraqi amphibious assault force that knifed its way east and south two days ago to besiege the Iranian oil center of Abadan and the oil port of Khorramshahr near the mouth of the waterway.

The fact that the artillery fire heard distantly from here for the past weeks has now faded and that there are few signs of troop movements or panic by authorities has convinced Basra residents that their government and its broadcast communiques are right, that Iraq continues to hold the initiative in the war, despite the damage inflicted on its oil industry here and elsewhere by Iranian planes.

"I think victory will be ours," the manager of the Hamdan Hotel in downtown Basra told a guest. "We have had enough of these Iranians. It is time someone taught them a lesson."