KABUL, Afghanistan (AP) _ The superpowers have left Afghanistan, but the fear, the fighting, the economic and social decay from their 12-year proxy war won't end anytime soon.

The United States and the former Soviet Union agreed to stop arming their warring clients - the Muslim rebels and the Communist-style government - by Wednesday. The Americans say they sent the last truckloads in October; the Soviets in mid-December.

But rockets are still being fired from rebel hideouts in the mountains that ring this city of 2 million, a reminder that for some time the arms cutoff will have no effect.

On Dec. 27, the anniversary of the 1979 invasion by the Soviet Red Army, the dull thud of incoming rockets and the bursts of machine-gun fire and government artillery echoed through the city.

Ghani Rahmanzai winced as the explosions rattled the windows in his cramped grocery shop in downtown Kabul.

''Please tell me what good it does,'' Rahmanzai said. ''They (the rebels) don't even know what they're hitting. It's always innocent people who die. They never hit soldiers or army positions.''

The government of President Najibullah rarely publicizes military casualties or damage to military targets, but there is no doubt most of the attacks are haphazard.

Even though Washington and Moscow have stopped military assistance, both sides have stockpiled enough munitions to keep fighting for another two years. Both sides will have little difficulty restocking their supplies.

Moscow agreed to stop supplying fuel used by Kabul's war machine. But diplomats say the government has stored enough fuel to keep its jets flying and the tanks rolling for months. They also confirm the government's claim that the former Soviet Asian republics have agreed to sell aviation fuel to Kabul.

Diplomats also say China has secretly offered to sell weapons to Najibullah's government. Beijing supported the rebels during the Red Army's nine-year occupation but abruptly stopped once the last of the 115,000 troops withdrew in February 1989. Chinese officials now fear a radical Islamic government in Kabul might one day try to stir up trouble in their border provinces.

The fundamentalist rebel groups, meanwhile, will be able to count on money and other assistance from the Muslim world.

Saudi Arabia, Iran and Pakistan provided arms and money to the rebels during the war but aren't bound by the cutoff agreement. Riyadh, Tehran and Islamabad are jostling to emerge as the dominant force in the region and their continued support for the rebels has prompted fears Afghanistan will become the battleground for an Islamic proxy war.

But most observers believe Najibullah's biggest headache for the moment is not the Islamic guerrillas, but the economy.

Pedestrians and bicyclists jam the city's badly rutted streets, a sign of the shortage of cheap fuel that also helps the poor heat their dried-mud homes properly.

Afghans don't hesitate to complain openly about the soaring cost of fuel, food and just about everything else. For most Afghans, it's a struggle to afford the basic staples of bread, tea and rice.

Recently, Prime Minister Fazal Haq Khaliqyar went to the markets to try to find out what was causing the surge. He was heckled and jeered.

The value of the Afghan currency, the Afghani, has dropped steadily since the Soviet withdrawal, straining the budgets of almost everyone including civil servants, who must get by on fixed incomes of about 6,000 Afghanis.

Residents, just as contemptuous of the rebels as the government, quickly dismiss the notion that the guerrillas are fighting for Islam or that they are likely to overthrow the government.

''Afghans want leaders who will look after the people instead of themselves,'' said Mohammed Sarwar, an observer at a government-sanctioned, pro-democracy rally in a downtown park Sunday.

The rally, organized by supporters of former Afghan king Zaher Shah, was broken up by young, bearded men who described themselves as ''Islamic students.'' They chanted ''God is Great 3/8 Death to America 3/8 Death to Zaher Shah 3/8'' slogans of the Pakistan-based fundamentalist groups.