In the twisting narrow canyons leading from nearby Pakistan, the honking Toyota pickup trucks career past plodding caravans of camels and horses -- all carrying weapons and Afghan guerrillas into the war against the Soviets.

Three months after a fierce Soviet and Afghan government offensive aimed to sever vital guerrilla supply routes here in mountainous Paktia Province, the Afghan resistance fighters, or mujaheddin, still swarm along the trails past this guerrilla base on their way to Afghanistan's northern and central provinces.

Both Afghan and western analysts say the continued operation of the supply system, despite Soviet efforts to cut it, represents the frustration of one of the Soviets' main strategic efforts during the past year of the war.

"These trails are essential to the jihad" (the holy war, or resistance), a guerrilla officer said during a recent trip through the area.

"We could not have continued the war if the Soviets had closed them," he said.

The heavy traffic on these rebel supply routes, following what may have been one of the bloodiest and most sustained battles of the six-year-old war, emphasizes the continuing inability of the Soviet Union and the Kabul government to defeat the insurgents -- and supports the expectations of rebel leaders that the fighting will remain intense during the coming winter monthsd

In November, and again early this month, trips along the Paktia supply routes were occasioned by an assignment in the interior of Afghanistan. Rebel fighters and refugees along the trail indicated that while the Soviets have increasingly harassed Afghans using the routes in recent months, not even their broad offensive of August and September has crimped the guerrillas' supply effort decisively.

Still, various rebel sources said even the marginal increase in difficulties along the trails has raised their transportation costs and their dependence on outside financial support, chiefly from Saudi Arabia and other Arab Persian Gulf states. Many rebels also said privately that they sometimes must sell weapons, apparently including those supplied secretly by the United States, to pay transport costs to their bases inside Afghanistan.

Together, Paktia and neighboring Nangarhar Province, to the north, offer the resistance fighters their most direct links from their arms and supply sources in Pakistan to three major areas:

*The capital, Kabul, and surrounding provinces, which are the scene of continual fighting between mujaheddin and Soviet forces.

*The central Hazarajat region, where the government and Soviets rarely contest guerrilla control, but where the mujaheddin have been fighting two Iranian-backed Shiite factions.

*The north-central region, from Sheberghan to Kunduz, which is the most distant and difficult for the mujaheddin to supply, and which suffers heavy attacks by Soviet forces operating directly from Soviet territory.

Although the Paktia offensive seemed largely designed to relieve guerrilla pressure against Soviet and Afghan government garrisons at the town of Khost, Afghan President Babrak Karmal promised that the drive also would seal the border against guerrilla traffic from bases in Pakistan. Soviet air attacks and commando raids against the rebels' base here at Jawar left bomb and mortar shell craters as reminders of the ferocity of the battle.

Earlier this year, the Soviets mounted a similar offensive on the border in Kunar Province, north of here, with the partial aim of closing guerrilla supply routes. A report by Pakistan's Institute of Strategic Studies suggested that as many as 10,000 Soviet troops may have fought in that campaign, and the institute's secretary, Noor Husain, described the closing of supply routes as a major Soviet objective during the past year.

Both guerrilla and western sources suggest that the Soviets have been more successful in closing supply routes into Kunar, notably through the establishment of new posts along the Pakistani border.

In November and early December, the trail in Paktia carried a heavy flow of two-way traffic: mujaheddin shouldering Lee-Enfield and Kalashnikov rifles, headed toward the Afghan interior, prodding pack animals loaded with arms and ammunition. Along the narrow mountain paths, such groups often had to stop to allow the passage of much larger caravans of refugees, usually from northern regions, near Mazar-i-Sharif or Kunduz.

On the twisting trails, the refugee caravans could be heard well before they could be seen. Men and children, climbing on foot when the trails became too steep for riding, shouted sharply at protesting horses.

The horses often carried all that a family had been able to take with them: mounds of multicolored quilts, clanking cooking pots and dangling kerosene lanterns. Atop the belongings sat veiled and silent women, often cradling their infants.

In some areas, local villagers support the refugees and mujaheddin, sheltering them in their homes or mosques. Where the route passes through sparsely inhabited mountains or regions where the population has fled, teahouses have sprung up to offer -- besides tea -- food, places to sleep, feed for animals and information about conditions on the trail ahead.

Small groups of mujaheddin specialize in supply missions and make the eight-day round trip from their base in Vardak Province, west of Paktia, to Pakistan several times each month. On the way into Afghanistan, an escort group of mujaheddin led several animals loaded with medicines, children's winter clothes and other supplies for the group's civilian supporters in Vardak.

"The [supplyz]trips are much more difficult now than a couple of years ago," Ruhani Wardak, leader of the escort group, said. The first night on the trail, the group divided into pairs to cross a broad plain south of Khost. Ruhani explained, "Now the shurawi Soviets use many more helicopters, either attacking from the air or landing special commandos to ambush us. So we travel in smaller caravans and walk more at night."

"We cannot defend against planes, so we only hide," he said.

Indeed, as the group arrived here from Pakistan in the crowded bed of a pickup truck, it heard the whispered roar of a Soviet jet still distant in the sky. Turbaned mujaheddin exploded from the truck in a tangle of arms and legs, boots and Kalashnikovs and scrambled for the safety of the base's nearby caves, while the several small trucks raced into dugout garages.

After the jet veered away, the men emerged from the caves, laughing at the false alarm. But three days later, the group of guerrillas crouched behind boulders in a broad, treeless valley, while two Soviet Sukhoi ground attack planes thundered low overhead to rocket a nearby campsite being used by a caravan of refugees.

The air quivered from the explosions, and smoke and dust billowed into the sky, but the refugees had scattered during the planes' initial reconnaissance run and suffered only a few injuries.

If air strikes are the most spectacular menace to the guerrillas' supply system, our first day's 12-hour hike quickly demonstrated more basic problems. When we finally stopped at a mountainside teahouse at 1 a.m., the only dinner to be found was a box of filthy mulberries and a few pomegranates, offered apologetically by the owner.

"Food is a special problem," Ruhani said, as we returned to the trail at 6 that morning. "So many of the villages along the trails have been bombed or mined, and the people have left. So there is no one to sell us food, or maybe there is only bread and tea."

The Soviet and government forces have also hampered the passage through Paktia, where they have managed to establish mountaintop posts overlooking easy routes, forcing the mujaheddin to switch to more difficult trails.

The mujaheddin have learned to vary their pace on the trail to confuse Soviet and government intelligence services, which may learn of their passage and try to set an ambush. On the trip in, crossing Paktia took only three days, walking an average of 13 hours each day while sleeping less than four.

The increased difficulties on the Paktia route, and further inside Afghanistan, have raised transportation costs for the guerrillas.

"A donkey or horse costs me eight times what it did two years ago," said Mohammed Sharif Ishaqzi, a commander from near Mazar-i-Sharif. "The Soviets cannot stop us from going into Afghanistan, but they are making it too expensive for us to take everything we need with us."