Between dawn and dusk, Barikot is a ghost town.

Along the deserted streets of this garrison settlement on the Afghan-Pakistani border signs of habitation are visible -- a row of Army trucks parked by an empty airstrip, laundry spread out to dry in a back yard, a few cows wandering untended. But for hours at a stretch no human movement is to be seen.

Sporadically, the eerie stillness hanging over a seemingly dead town is broken by a short burst of heavy machine-gun fire as Moslem guerrillas dug in on the ridges overlooking the settlement open up on a suspected target. Then the echoing gunfire dies away, and the silence of the mountains returns.

The guerrillas, or mujaheddin, have had Barikot and its Kabul government garrison encircled since September in a bid to capture the border town at the head of the Konar Valley. Barikot's land links with the capital have been cut for more than two years.

Today the siege shows few signs of reaching an early end, and it is becoming an increasingly volatile flash point on the troubled border. In recent months, Pakistan has lodged repeated charges of Afghan Air Force overflights of its territory and several incidents of bombing of the Pakistani town of Arandu, about a mile across the border from Barikot. Kabul has retorted with countercharges of stepped-up Pakistani support for the mujaheddin and of shelling of Barikot from Pakistan.

In comments to journalists in Peshawar Friday, Pakistani President Mohammed Zia ul-Haq described the increase in violations of Pakistani airspace as "unhealthy," adding that Kabul should realize that there is a limit to Islamabad's tolerance.

Zia, who was in Moscow for the funeral of Soviet leader Konstantin Chernenko Wednesday, was issued a stern warning about Pakistan's support for the Afghan rebels by the new Soviet leader, Mikhail Gorbachev, the Soviet news agency Tass reported Friday.

During the winter months, Soviet and Afghan government troops have made a concerted effort to push up the Konar Valley -- a perennial focus of anti-Kabul resistance -- apparently with a view to both breaking the siege of Barikot and establishing strongholds along the valley that would hamper guerrilla infiltration and supply. With the coming of spring, the valley that runs parallel to the Pakistani border is becoming one of several major supply conduits from Pakistan to the resistance across Afghanistan.

The winter offensive appears to have failed dismally. A large Communist force that began advancing from Jalalabad in mid-December succeeded in reaching Chaghasarai, the provincial capital of Konar, and later pushed on as far as the town of Asmar, meeting resistance at several points. But in February the advance stalled amid heavy fighting just beyond Asmar, about 25 miles short of Barikot.

In late February and early this month, posts established following the Communist advance were destroyed piecemeal by mujaheddin groups operating in the now largely depopulated valley.

"The situation is back much as it was at the begining of winter," noted one western diplomat. The guerrillas have built well-camouflaged bunkers and gun emplacements on ridges dominating the town on both sides of the valley. Barikot is now wholly reliant on resupply from the air. But with the resistance fielding an impressive concentration of heavy machine guns on the heights, that is becoming an increasingly hazardous undertaking.

According to mujaheddin of the Peshawar-based National Islamic Front of Afghanistan, the last supply drop came more than one month ago as transport helicopters under heavy fire from the heights dumped food and ammunition without even touching down. Despite covering fire from attack helicopters and bombing by jets, one transport was downed, crashing just clear of the airstrip.

With the failure to lift the siege by land last month, repeated attempts have been made in recent days to knock out mujaheddin bunkers on the mountaintops to facilitate the ferrying in of supplies by air. Predictably, the stepped-up air attacks have resulted in further charges from the Pakistani government of overflights and bombing of Arandu. For their part, the Kabul authorities contended late last month that hundreds of men had crossed the border to attack Barikot, one of a string of similar accusations dismissed by Islamabad as "fictitious."

Both sides' charges appear to have considerable justification, however. On Tuesday MiG23 jets supported by Mi24 and Mi8 helicopter gunships could be seen bombing and rocketing mujaheddin positions around Barikot, and, at the end of their attack runs, clearly overflying Pakistani territory.

Guerrillas later said that machine-gun fire from the helicopters had hit houses on the Pakistani side of a narrow mountain stream in the Arandu Valley that marks the border. But less easy to gauge was whether the overflights were deliberate or more or less inevitable, given that mujaheddin positions overlooking Barikot are about a half-mile from the border.

The following day, according to Islamabad, Afghan jets dropped 37 bombs on the Pakistani side of the border, and on Thursday another raid reportedly killed two persons near Arandu.

It is clear that under cover of darkness, large groups of guerrillas are moving through Arandu to cross the stream and reinforce positions around the Kabul government's beleaguered garrison.

"Some of our groups are fighting inside more or less permanently," said Mohammed Ayub, a commander from the Asmar area. "But many others will go in from the camps to fight for two or three months and then return to their families as other mujaheddin take over." With the snows melting fast, increasing numbers of fighters are now moving back into Afghanistan.

Around Barikot itself, the siege drags on at an almost medieval pace. Guerrillas while away the time sniping at an occasional Afghan Army soldier emerging from cover.

On one afternoon a group of guerrillas were observed around a new Chinese heavy machine gun. They were greatly amused as they terrified a man foolhardy enough to attempt to drive a stray cow back into a pen. Clearly visible through binoculars -- and the machine gun's telescopic sights -- the man finally lost his nerve and sprinted for cover as bullets peppered the ground around him. He escaped unscathed, but others have been less lucky.

For Barikot's population -- a force of about 1,200 soldiers, 300 militia and 2,000 or 3,000 civilians -- conditions are deteriorating. According to accounts from the besieged town reaching the guerrillas, food prices have spiraled, meat is now rarely available and morale is low. During the day, the population remains indoors, emerging after dark to go about normal business, including working in the fields within the defense perimeter. Any use of lights invariably attracts guerrilla fire.

Nor does the garrison exert itself much in its own defense. Outposts on the lower slopes keep attackers at a distance, but there are no attempts to venture beyond the town's defenses and try to dislodge the guerrillas from their positions on the heights.

On their side, the guerrillas display little determination to bring the siege to an end. Mirroring the situation around hundreds of Afghan Army and Soviet posts across Afghanistan, the resistance effectively has succeeded in bottling up Communist troops and gaining a tactical initiative. But lack of heavier weapons and, in many cases, of political direction results in an inability to exploit the advantage.

At Barikot, the guerrillas cite mines laid around Communist defenses as the main reason for the current standoff. But an element of lethargy is discernible, too. In contrast to aggressive assaults through mine fields witnessed last year in the Panjshir Valley, there is little evidence at Barikot of readiness to risk casualties in a concerted effort to seize the town.

But the underlying weakness of the resistance in the Konar Valley is its solidly tribal composition, which inhibits the establishment of a unified command and makes military coordination difficult. Around Barikot, at least five major Peshawar-based mujaheddin parties are represented by different Pushtu tribal groups.

Pushtu tribal allegiances remain paramount and effectively preclude the emergence of the sort of regional commands that have proved highly effective in the ethnically Tajik and Uzbek provinces of northern Afghanistan, where society is not tribal.

"One tribe here would never accept the leadership of a man from another," noted one Peshawar-based analyst, himself from the Konar Valley, a bastion of Pushtu conservatism.

Such as it is, coordinated military decision-making around Barikot and Asmar is arrived at by means of a jirga or assembly of tribal leaders. The result is generally more talk than action. Even when it does occur, coordinated military action hinges mainly on intertribal competitiveness, no one tribe wishing to have its honor stained by appearing less warlike than its rivals.

Around Barikot at present, there is talk of a jirga to decide details of a final assault on the embattled and dispirited Communist enclave. But observers are not holding their breath waiting for the big push.