Most of the Soviet troops occupying Afghanistan appear to have made special efforts to be polite and create a good impression on foreigners here, offering an image of an invasion with a human face.

A number of reporters have been detained by Soviet troops, however, for venturing too far into the countryside or photographing Soviet installations.

While some have been treated to lunch and merry-making at Soviet camps, other journalists have been force to stand for hours in the snow and treated roughly.

One American television crew drew warning bursts of automatic rifle fire over their heads outside Kabul. Still, the recent reception of three Western reporters seeking entry to Kabul's hilltop Bala Hissar fortress was more typical.

"To what do we owe the honor of your visit?" the Soviet Army commandant asked. A tall, imposing man of about 35 was a large pleasant face and rosy cheeks, he listened patiently as a Russian-speaking member of the group offered the rather feeble explanation that the ancient fortress, with its high stone walls and turrets, was of enormous interest to tourists.

"It's in all the guide books," he was told.

Built in the late 19th century by king Abdur Rahman Khan, the fortress was the scene of past fighting involving the British and has figured prominently in Kabul's history during the past 100 years. Perhaps because of its importance for control of the capital, the moated citadel is more visibly guarded by Soviets than other installations here.

Our initial approach to the fort had provoked a rather cool reception but the atmosphere gradually warmed.

A half dozen young Soviet soldiers, armed with Kalashnikov automatic rifles and obviously Europeans, guarded the fort's entrance, a street-level gate to a snow-covered road that leads up to the hilltop fortress. A light tank, partly concealed, stood on the side of the road about 30 yards inside the gate.

A week before, only two soldiers, had guarded the gate and no tank was visible. Now the soldiers seemed much more alert and serious, carefully watching the street in front of the gate and occasionally opening it to let Soviet trucks in or out.

"You can't go up," one soldier said.He added that the place had been "closed" since Dec. 28, the day after the Soviet-engineered coup that installed a new puppet government here.

He agreed, however, to ask a higher authority, and another soldier trudged up the hill through the freshly fallen snow. Efforts at small talk during the wait for his return drew only grunts and vacant stares.

Eventually a soldier with a blond mustache and pale blue eyes descended, listened to our request and invited us to come through the gate and stand under a shelter just inside. Like the others, he wore no insignia on his Soviet Army jacket.

Another superior was sent for, and a while later three more soldiers came down the hill, a Caucasian and two Asians.

"This is a military site," the Caucasian said. "If you know anything about military affairs, you know you can't go in."

Our argument that the fort was of tourist interest eventually resulted in another shuttle up the hill.

About 15 minutes later, three more Soviets came down the hill. The tallest one announced in light-hearted colloquial Russian, "I am the commandant of this show." The other soldiers and officers -- by now about a dozen had gathered -- grinned to each other and began to relax.

The officer had an easy manner and a self-confident air. Unlike the soldiers, he wore a tan tie under his jacket and a holstered pistol on his belt.

After carefully reading our press passes while an aide jotted down names and passport numbers, the officer said wryly, "Unfortunately I have to disappoint you. This is a military site and I couldn't possibly let you in without instruction from higher up." He added brightly, "But you could try to arrange it through your embassies."

We shook hands all around and he escorted us to the gate. As we were walking toward our taxi, he called out, "Let me wish you a happy New Year and, oh, and a happy Christmas."