Winter snows have begun to enforce an uneasy truce around the Afghan capital as insurgents fighting Soviet and government troops have pulled back into the mountains or across the border to bases in Pakistan.

But the Islamic Mujaheddin guerrillas have mounted increasingly effective defenses against the Soviets and have carried out increasingly daring raids into Kabul during the past three months as their three-year-old war against the government of Babrak Karmal has intensified.

A reporter who traveled with the resistance forces into Kabul returned from the raid convinced that at least one group within the Mujaheddin is capable of launching major attacks on government buildings and military posts inside Kabul.

The one I witnessed occurred on Sept. 30, when a military transport depot in the Shahrenaw or new district of the city was totally destroyed. The operation, carried out by 37 insurgents, took place not much more than a mile from the old city center. The huge flames must have been visible in most of the city.

The attack lasted well over an hour and the insurgents overran one small, street-corner bunker before reaching their main objective. By the end of the night, 42 vehicles, mostly Soviet-made Zil151 and Zil157 trucks and modified tanks had been transformed into blackened wrecks after the depot's gas station exploded into a huge ball of fire that reached high into the clear, moonlit sky.

The 37 Mujaheddin who mounted the attack were part of the 300 men at the disposal of local commander Zabit (Lieutenant) Abdul Halim. The various bases in which the 25-year-old commander has spread his men are a development of the past year. In that time, his band has pushed back the control of the government by successfully attacking the various military posts in the farthest outlying outskirts of Kabul. Their successes have given the insurgents more room to maneuver in areas they term "liberated" and where they can at least count on the support of the local population.

It was from one of these villages that the Mujaheddin set out in the early evening a month ago, four men out in front as a forward guard, the other 33 marching in a long line of dark shadows behind.

Although Zabit Halim has done a good job of forming the individualistic Afghans into something resembling a trained guerrilla force, one year has not proved sufficient to iron out all the problems.

As Halim called his men to a halt in the corner of a field, chose the password of the night and ordered all weapons loaded, a shot went off -- the first security breach. It was serious, for by that time sporadic gunfire could be heard from more than one of the brightly lit Army posts to the north. The Mujaheddin continued across the open, harvested fields, past the first military posts and on into Kabul.

Kabul has grown through the huge influx of refugees from villages attacked by Afghan and Soviet troops, and before entering into the built-up urban center our group passed hundreds of tents whose occupants seemed to own as many dogs. A high-pitched wailing and barking announced their arrival.

Aernout Van Lynden, a Dutch free-lance journalist who has previously written from Afghanistan for The Washington Post, sent this dispatch by courier from an undisclosed mountain base on Oct. 10.

Suffering from the Afghan inability to keep one's own presence a secret or one's voice down, the group was detected shortly after entering the city proper. Heavy, inaccurate machine-gun fire rent the evening.

It was 9:45. Curfew was not yet in force, but the streets were deserted. The Mujaheddin, returning the fire , dashed from street corner to street corner, seemingly well aware of their task. In fact, it took all of Halim's authority to control his men.

Making maximum use of the megaphone, part of the standard kit of most Afghan insurgent groups, Halim -- in a voice that would put the fear of God in any man -- drove his men forward, simultaneously issuing stentorian warnings to the soldiers opposing him and his men.

The megaphone served its purpose: a military street-corner bunker on the route to the transport depot was deserted by the time the first insurgents reached it and set it afire.

By this stage, the Mujaheddin were well inside the city and were being fired on from almost all sides. This slowed them down, but did not deter Halim. At 10:30 the first of the 42 vehicles was set on fire. It proved a somewhat tedious process because the insurgents' home-made explosives failed to go off. Six insurgents then had to use their Soviet-made AK47 assault rifles and -- more conventionally -- matches.

As the fire spread to the whole depot, any semblance of a disciplined attacking force was lost. The Mujaheddin were jubilant and the bottled-up fear and tensions were released in cries of triumph. Wildly shouting their devotion to God, their hate of the God-less Showrais (Soviets) and their belief in the inevitable victory of Islam, the Mujaheddin began their withdrawal as the night was transformed by a somewhat frightening carnival-like air.

By 3 a.m., the insurgents were back in the caves of their mountain base at Yagh Dara, congratulating themselves on an operation completed successfully and without casualties.

The most important question raised by the evening's operation is why neither Afghan government forces nor their Soviet counterparts launched any effective action against an attack inside a built-up urban center that lasted more than an hour.

The Afghan Army is grossly understaffed, badly overextended and generally demoralized, the nationalist forces maintain. The various Afghan units appear to do their utmost to stay in the comparative safety of their posts. This was asserted to this correspondent by an active-duty Army officer and several conscripts who have defected.

[Diplomatic observers and analysts based in India and in Pakistan share this assessment of the Afghan Army, William Claiborne of The Washington Post reported from New Delhi.]

The lack of Soviet initiative suggests to observers a reluctance of Soviet commanders to deploy their men in combat situations initiated by the nationalists rather than by Soviet forces. This is particularly true at night, when ground forces cannot count on the support of MI24 helicopter gunships.

Since the attack a month ago, there has been a marked effort by the authorities to strengthen security around the capital. Various units, both Afghan and Soviet, have been redeployed from the provinces to bolster posts in the capital and to launch counterattacks.

[Significant Soviet setbacks were reported in ground offensives last month in the Panjshir Valley, 60 miles north of Kabul, and the town of Paghman, 9 miles north of the capital. Both are guerrilla strongholds, according to diplomats in Washington and New Delhi.]

The new security measures around the capital have been partially successful. Zabit Halim has been forced to make a tactical withdrawal into the mountains 30 miles to the south of Kabul and other Mujaheddin have pulled back for the winter.