The stench of death still lingers in the shuttered streets of the South Yemeni capital, but rebel forces have crushed all opposition by the forces of deposed strongman Ali Nasser Mohammed and are consolidating their authority after the brief but devastating civil war in the Middle East's only Marxist state.

A new provisional government under interim President Haider Abu Bakr Attas, who was prime minister under Mohammed, is in full control of Aden and claims to have authority throughout the countryside, including the key province of Abyan, Mohammed's last bastion of support.

The port of Aden, littered with the blackened hulks of sunken vessels, reopened Sunday. By Monday, the first planeloads of food and medical supplies were arriving from Moscow aboard special Aeroflot flights.

This correspondent and three others were the first foreign journalists to reach Aden following the fighting. After a three-day crossing of the stormy Gulf of Aden from the east African nation of Djibouti in a 35-foot yacht, we covered the last six miles in a rubber dinghy, spending Monday night on the water when denied permission to land. Permission to go ashore was granted yesterday.

We found a capital still bearing the scars of nearly two weeks of fierce fighting that was touched off, according to authoritative sources here, when Mohammed tried to eliminate his political opponents in a preemptive attack Jan. 13.

The number of dead is believed by local observers to exceed 12,000. The bodies have been buried in two mass graves, but the stench of rotting flesh still pervades many areas of the city.

"It was hell. The shells and bullets were coming in from everywhere," said a South Yemeni port official who asked not to be identified by name.

Troops and turbaned tribesmen patrol the largely deserted streets, flashing victory signs at one another and supervising the slow work of removing the debris of war: the twisted hulks of tanks and armored personnel carriers, the burned-out cars and trucks, the rubble of bombed buildings and thousands of spent shell casings.

The area around the port of Aden, known as Steamer Point, has been almost entirely destroyed. A Panamanian tanker, the Cosmos, lies on its side half under water. It was sunk in the harbor by the cross fire of a fierce battle between rebel tanks and naval gunboats loyal to Mohammed.

Another tanker was badly damaged and an Australian yacht, named the Innocent Bystander, also was sunk.

The Steamer Point area, the site of government offices and a naval base, was the scene of some of the heaviest fighting, although the port facilities themselves remain intact. Most of the shorefront buildings, however, have been reduced to rubble. Thick slicks of oil from two damaged storage tanks coat the streets.

Teams of workers are spreading sand on the oil and hauling off the hundreds of damaged vehicles. Shops are slowly starting to reopen while armed patrols check the identities of motorists at roadblocks throughout the city.

Efforts to restore water, electricity and other essential services are continuing. A four-member team from the International Committee of the Red Cross arrived from Djibouti yesterday with a ton of medical supplies.

Local officials, speaking on the condition of anonymity, gave the first authoritative accounts of how the fighting started and the reasons behind it. They also said that about 1,200 foreigners remain in Aden following the evacuation of most foreign nationals to Djibouti by British, French and Soviet ships last week.

Those who stayed behind include about 1,000 Indian oil refinery workers, some Soviet and Arab diplomats and 12 Filipino hotel workers who said that they had no money with which to leave.

According to the local officials and several neutral sources, the fighting erupted on the morning of Jan. 13 when Mohammed, fearing a move to overthrow him, called a meeting of the 11-man Politburo and tried to execute four of his chief rivals.

When the Politburo members arrived at the Central Committee headquarters in the Steamer Point area, presidential guards fired on them, killing Vice President Ali Antar and former defense minister Saleh Muslih Qassem, the sources said.

Former strongman Abdel Fattah Ismail, who returned from five years in exile in Moscow last fall, was wounded in the arm while Ali Salem Bedd, minister of local affairs, escaped injury, according to the sources.

Just before the shooting, senior officers loyal to Mohammed had begun rounding up other commanders known to be supporters of Ali Antar and "just mowed them down in their barracks," one authoritative source said.

The fighting spread quickly after that, as the military split and armed tribesmen loyal to the various factions controlled by their kinsmen descended on the capital from the surrounding hills, the sources said.

"The president Mohammed had the senior officers, but had almost no support among the middle and lower ranks," one source said. "Ali Antar's supporters also had the tanks and the rocket forces, and around the third or fourth day, these proved to be decisive," turning the battle in favor of the rebels.

The source said that Mohammed apparently had planned his preemptive strike much earlier because "sacks full of pamphlets denouncing Ali Antar and Ismail for plotting a coup" were later found by the rebels.

However, "the president apparently underestimated the resistance and the reaction to the barracks massacres," the source added. "If he had just killed the politicians, he might have gotten away with it. But the fighting spread quickly when they started executing commanders at the lower levels, because then everybody had to fight desperately to survive."

While this version of events could not be confirmed independently, it reinforced the impression of diplomats and other neutral observers that the fighting spread spontaneously, taking the Soviet Union, which maintains a large military and diplomatic presence here, by surprise.

While Mohammed and his rivals are all Marxists, Ismail and his supporters apparently take a harder line. They reportedly were strongly opposed to Mohammed's efforts to improve relations with some of the conservative Arab nations such as Saudi Arabia.

In the beginning, Moscow seemed to support Mohammed, but when his forces quickly began to crumble in the city, the Soviets tried to avoid taking sides, diplomats said.

The Soviet Embassy was shelled and badly damaged by Mohammed's forces in apparent retaliation for Moscow's lack of support, local officials said.

Authoritative sources added that Moscow is supporting the new government now that it appears to be firmly in control.

The composition of the new government, however, is still not clear.

Attas, who was in India and then flew to Moscow when the fighting erupted, returned Monday to head the new government in line with an agreement secured by Moscow among the rebel factions.

However, he is described by one knowledgeable source as a "compromise interim figure" while the new government, which is being called the "collective leadership," is being formed.

"There was quite a lot of killing and destruction and these people are now regrouping and trying to organize themselves into a government again," the source said.

Reporters were shown a prison where 150 political opponents of Mohammed were said to have been machine-gunned to death in their cells Jan. 15 and then buried in a mass grave.