More than 20 persons were killed here today in violent fighting between Iranian Arabs seeking autonomy and forces loyal to Ayatollah Urhollah Khomeini.

Army reinforcements were rushed here from Tehran and, according to evewitnesses, Iranian naval vessels fired from the waterfront into the city in an effort to put down what appears to be the most serious challenge so far to Khomeini's rule.

A state of emergency was declared by the provincial governor, Ahmad Madani, a rear admiral who also heads Iran's navy. Late tonight, bands of armed men were ignoring Madani's curfew order, and scattered shooting continued.

In a day of violent clashes, armed Arabs attacked a naval base, the central police station, government buildings and shops, leaving many buildings burned and damaged.

Government radio said 21 persons were killed and 76 injured in Khorrashahr, but residents put the death toll at 40 or more.

[Fighting also broke out in Abadan, a neighboring oil refinery city, between Arabs and government forces, news services reported. Paratroops reportedly were flown into Abadan to assist local forces there and in Khorramshahr.]

The clashes between the Arabs, who number about 2 million in this country of 35 million people, and the predominantly Persian followers of Khomeini marked the latest conflagration in Iran's provinces. Ethnic minorities demanding autonomy have fought pro-government forces in several sections of the county.

Authorities fear that the fighting, which in some cases has also pitted right-wing Moslems against leftist elements, represents perhaps the greatest threat to Iran's stability and risks plunging the county into more widespread civil strife.

Since central government authority broke down during the revolution against the shah, clashes have occurred in Ir faces.

Racial discrimination on Washington's selet th fighting in the oil-rich southwestern province of Khuzestan - which its Arab residents prefer to call Arabestan - appears to be the most serious yet, verging on an Arab insurrection against government authority centered in Tehran and Qom.

Blaming Khomeini's Revolutionary Guard for provoking the fighting, Ayatollah Taher Shobeir Khaqani, the leader of the region's predominantly Arab population, called for the governor's dismissal and warned that he would not be able to control his followers if the conflict continues.

Khaqani also threatened to order his followers, who comprise much of the region's oil work force, to go on strike unless Arab demands are met.

According to Arab residents here, today's clashes broke out before dawn when Khomeini's Revolutionary Guardsmen stormed two building occupied by protesting Arabs and killed several of them. Armed Arabs then attacked government buildings in retaliation.

The scene on the highway into the city recalled the battle for Tehran during the insurrection that overthrew Iran's monarchs in February.

Ruins of burned-out buildings smoldered on either side of the road, which was littered with charred debris left by the passage of rioting mobs. Gutted cars were still burning by the road.

Pickup trucks and ambulances took the dead and injured to hospitals or to burial. In the back of one pickup truck lay a body covered by a black cloth and ice packs to help preserve it in the steamy 109-degree evening heat. Two Arabs sat with the corpse and wailed their grief.

A road leading into Khorramshahr was guarded by revolutionary militiamen, wearing camouflage uniforms and green berets, who had been flown in from Tehran earlier today.

Beyond their check point, automotic weapons were fired toward our car full of Western journalists, forcing us to stop and take cover.

When the firing stopped, Arab youths ran up to pour out their grievances against khomeini and his revolutionary committees.

"We've trying to stop the committees from taking over," said one. "We don't want to spit from Iran. We want autonomy that's all."

Another called the army "fascist" and said it had no changed since the days when it obeyed Shah Mohammad Reza Pahlavi. "The commandos are againt us," he said referring to the Revolutionary Guards sent to join local Army and Navy forces in quelling the disturbances.

"The Iranians brought guerrillas in to kill the Arabs," he said. "They have been killing people one by one. But we will not sit still. We will destroy them."

A few hundred yards away, excited Arabs armed with rifles, pistols, knives and clubs searched our car before allowing it to pass. Only a few blocks beyond that was a check point manned by street fighters loyal to Khomeini and Madani. One youth, his face covered by a white cloth, stood with a grenade in his right hand while others, led by a frantic Iranian armed with a revolver, again searched the car.

The drill was repeated at another road block, this one again Arab-controlled, near Ayatollah Khaqani's house.

Aides said Khaqani had worked out an agreement to end weeks of simmering unrest in the region after visitingg Khomeini in the holy city of Qom on Sunday. They said that representatives of Khaqani conferred with Madani until 3 a.m. today and reached an agreement for the evacuation by Thursday of two building - a former U.S. consular office and an Arab cultural center - occupied by automony-seeking Arabs.

But an hour after the meeting ended, the aides said. Revolutionary Guards attacked the building.

In an interview at his home, Khaqani said he was prepared to renegotiate a cease-fire between the Arabs and the government. "Otherwise I am afraid I will lose control of the whole situation and it will become a bigger fire," he said.

Asked about eh possibility of a strike by Arab oil workers, Khaqani siad, " So far I have not asked for a strike because we want to settle this peacefully. But if the government doesn't want to act according to the rules of Isalm, then perhaps the Arabs will have no other alternative."

Speaking in Arabic through an interpreter, the white-bearded religious leader blamed the latest clash on Admiral Madani, who was shifted to the sensitive Khuzestan post from his previous position as the Khomeini government's first defense minister.

"His presence here is an explosion," Khaqani said. "If he stays any longer, th fighting will continue. The government should replace him with another man as soon as possible."

"My final word is to strongly suggest that the government stop this [fighting] and come to an amicable agreement with the Arabs because I fear the Situation will become very dangerous and impossible to control."

As he spoke, his brick residence came under automatic weapons fire. Aides said afterward that two guards posted on the building's sandbagged roof had been hit by snipers and were rused off to a hospital. CAPTION: Map, no caption, By Dave Cook - The Washington Post