On the snow-topped mountains and in the remote sunless valleys of eastern Afghanistan, stubborn Moslem tribesmen are fighting a sputtering but determined war of resistance against the country's leftist government.

It is one of the least accessible conflicts of modern times, a hit-and-run campaign in mountain-goat terrain where there are few roads and no telephones.

In Afghanistan's capital, Kabul, the government tries not to acknowledge what is taking place.

Even here in the capital of Nungrahar Province, site of a major air base, there is little sign of the fighting in the mountains just to the north. But there are troops at every bridge and tunnel along the main road east of here and a camel corps detachment is stationed at the entrance to the Khyber Pass.

According to sketchy accounts available here and in the Afghan refugee center of Peshawar, across the border in Pakistan, a classic guerrilla war is unfolding, matching shrewd, determined local warriors with limited weapons against the jets and artillery of the Soviet-trained Afghan armed forces.

This vest-pocket war may be unique in that it pits deeply conservative, devoutly religious guerrillas against a leftist government trying to establish its revolutionary program in the hills as it has in Kabul.

The tribesmen are resisting, just as they resisted 50 years ago when the king of Afghanistan tried to force them to unveil their women. This time they are said to be even more determined because they consider themselves to be defending Islam against atheists.

Even more than other such conflicts, it is a war without statistics and a war without reliable accounts of what is happening. The government, insisting that the entire 225,000-square-mile country is secure, gives out no reports on the fighting, and the rebels have no central headquarters and no radio transmitter.

Two rival groups of Afghan exiles, operating out of bare, chilly offices in reeking alleys in Peshawar, claim leadership of the resistance.

Their occasional press releases contain what appear to be exaggerated and self-serving statistics -- 1,197 government soldiers killed, three helicopters downed. But their contacts with the estimated 30,000 Afghan refugees in the Peshawar area and regular visits from fighters who cross into Pakistan's Northwest Frontier Province in search of arms provide much of the information available on the conflict.

One of the groups is the Islamic Society of Afghanistan, headed by Burhanuddin Rabbani, 38, former professor of Islamic theology at Kabul University. The other is the Islamic Party of Afghanistan, led by Gulbuddin Hekmatyar, 32, a former engineering student.

Both claimed in recent interviews to be in overall command of the insurgency. They denounced the Kabul government of Premier Nur Mohammed Taraki as communistic, atheistic and repressive, and said they are trying to turn the hill country resistance into a nationwide campaign to oust Taraki in favor of an Islamic republic, like Iran.

Experienced observers of Afghan affairs, however, say it is doubtful that the guerrillas are taking orders from anyone or that they really care much about who is in power in Kabul.

Pathan tribesmen, who live on both sides of a border that has traditionally meant little to them, have a long history of resistance to control by any central government. Many observers believe they would be content if the Taraki government would merely leave them alone instead of trying to send in troops and cadres to impose the tenets of Taraki's Soviet-style revolution.

If the Pathans succeed in reasserting the independence of their local villages, it is questionable whether they can be mobilized for a national campaign to bring down the Kabul government. The danger for the Taraki government is not that the guerrillas will move closer to the capital but that the concept of resistance and the possibility of success will inspire similar outbreaks in other parts of the country.

The center of the resistance is in Kunar Province, the next one north of here, in a region known as Nuristan. The tribesmen there were only converted to Islam in the 19th Century and are now said to have a convert's zeal in opposing a central government that makes little attempt to hide its antireligious sentiments.

Armed clashes in Nuristan have apparently resulted in substantial casualties and defections among government troops. The government has responded with air strikes but the planes have few rewarding targets in a region without population centers.

The conflict, although generally confined to four provinces along the Pakistan border, gives some signs of spreading and is taking on regional implications.

Although Pakistan, a Moslem country suspicious of the Kabul government, has officially disassociated itself from the rebellion, it allows the dissident organizations to operate in Peshawar. Pakistan says it is incapable of stopping arms traffic across the long, mountainous frontier.

Both the Afghan government and the dissidents appear dissatisfied with this -- the government because Pakistan is not doing enough to control the rebels, the rebels because Pakistan will not give them arms and funds or allow them to make radio broadcasts across the border.

Afghan Foreign Minister Hafizullah Amin told Western correspondents recently that "without foreign interference, there would be no such counterrevolutionary activities in Afghanistan. Our revolution is a people's revolution, completely and sincerely supported by the people of the country. There is no resistance to our revolution whatsoever. But we have documents to confirm foreign interference."

He would not name the source of the alleged interference, but it was understood that he meant Pakistan.

Iran is not yet directly involved. But the recent success of the mullahs' rebellion there has lifted the spirits of the Islamic society and the Islamic Party and perhaps of the fighters in the hills as well.

Rabbani said the Islamic society is considering a direct approach to the new Iranian government to appeal for aid on religious grounds. Iranian aid to the Afghan rebels might prompt the Kabul government to stir up trouble inside Iran, escalating the entire conflict.

According to reports on the conflict picked up here, in Kabul and in Peshawar, the traditional Pathan resistance to outside authority developed into armed conflict after the pro-Soviet coup that brought Taraki to power last April.

"They're holding out against an alien, atheist program," one informed source said. "It's not the social aspect they object to, the land reform, but the antireligious aspect."

Recent arrests by the Kabul government of prominent religious figures are reported to have reinforced the tribes' determination to resist.

Senior diplomats believe that government troop losses amount to several hundred at least and that the rebels have been building up their strength with captured weapons. The rebels have no known regular source of arms and ammunition, but there are reliable reports of purchases on the thriving Pakistani market.

Experienced observers in Kabul and Peshawar say the insurgency is a constant annoyance to the Taraki government and is inflicting losses of life, equipment and morale on the country's conscript army.

But, they say, it does not yet threaten the central government's grip on power in the rest of Afghanistan, and will not unless the resistance spreads in scope and intensity. For that the movement appears deficient in motivation, funds, leadership and international support -- the commodities that the exile groups in Peshawar are now trying to provide.

At least one of the groups, the Islamic Society, has developed to the point where it is running refugee camps that may also be used for training guerrillas and is able to arrange visits for journalists willing to put in two weeks to travel to rebel areas of Kunar.

The rebel commander there, Rabbani said, is a tribesman identified only as Obaidullah, who has surrounded himself with tough and well armed subordinates and claims to have taken scores of prisoners. That claim is supported by photographs said to have been taken in Kunar showing young men identified as soldiers under the guard of rebel fighters.

Although diplomatic analysts say the rebel movement suffers from the lack of a prominent figure who could be identified as a leader and guide for the insurgents, Hekmatyar said that is not actually a weakness, only an indication that the insurgency is still in an early stage.

"A year ago," he said, "who ever heard of Khomeini?"