Resistance fighters in a hide-out in Afghanistan once were bewildered to hear a radio report that their forces had attacked the second most important Soviet air base in the country. The broadcast said that the insurgents had poured gasoline into drainage ditches, set the fuel afire and triggered a series of explosions that lasted two days.

The report, which quoted "diplomatic sources" in the Indian capital of New Delhi, was not true. The anti-Soviet mujaheddin, or guerrillas, were not involved. A soldier at the base itself had blown up an ammunition dump to protest the appointment of a prime minister whom he did not like, according to resistance sympathizers working at the base.

Because of journalists' difficulties in getting first-hand information about the war in Afghanistan, media briefings by Western embassies outside the country have become a major source of data about what is happening there. The briefings are based on reports by Western diplomats stationed in Kabul, but the envoys there are severely restricted in their own information-gathering and acknowledge that there is no way to confirm much of what they pass on. As a result, reports about events outside the capital occasionally have proved to be highly inaccurate.

"You could almost say that the briefings have become a sort of new Five O'Clock Follies," said one disenchanted Western diplomat, referring to the U.S. military's 5 p.m. briefings in Saigon during the Vietnam War. "We're citing casualty figures which we have no hope of confirming or checking."

Precise information about Afghanistan always has been scarce, but this seldom was considered important before the Soviet intervention three years ago. The world suddenly wanted more data about the Soviets' first drawn-out military campaign since World War II.

The embassies' difficulties are illustrated by the handling of the accident that is said to have occurred in the strategic Salang Tunnel at the beginning of November. The story was broken by diplomatic sources and referred to deaths of 700 Soviets and 400 Afghans from asphyxiation because of fumes released in the tunnel following a collision involving a fuel truck.

Resistance commanders and party officials in Pakistan, while confirming that something of importance had happened in the tunnel, said that as far as they knew between two and 400 people had died. The difference in estimates is noteworthy because resistance sources are widely believed to inflate figures on enemy casualties. They are said to add at least one zero, reporting 100 dead instead of 10, for instance.

After the Soviets' Christmas Eve invasion in 1979 to combat a growing Moslem insurgency and to install Babrak Karmal as president, hundreds of journalists descended upon Kabul. They were not allowed to remain for long, however, and all foreign correspondents were forced to leave by the end of February 1980. With only occasional exceptions since then, visas have not been issued for Western journalists.

As a result, the only direct coverage of the escalating war has been by journalists willing to risk entering Afghanistan with a group of insurgents from neighboring Pakistan, where the resistance set up a capital-in-exile in the city of Peshawar.

The sheer physical and logistical difficulties that such trips entail, particularly for television, soon caused much of the initial interest in covering the war to fade. It takes four days of hard marching through the country's mountainous terrain to travel from the Pakistani border to the outskirts of Kabul. Journalists, including this correspondent, have continued to cross into Afghanistan with the insurgents, but the number is decreasing every year.

At this point, certain Western governments stepped in. Sensing that the war was in danger of disappearing from the general public's attention, they ordered their embassies in New Delhi and Islamabad to hold weekly briefings for the press about the state of the war as part of an effort to keep alive the issue of the Soviet intervention.

The briefings are based on the "sitrep," or situation report, sent by embassy staff still present in Kabul. The United States, Great Britain, France, West Germany, Australia -- to name a few at random -- still have foreign service personnel stationed in Kabul despite their refusal to recognize the legitimacy of the Babrak government.

The briefings have become a weekly news event in themselves. The briefer lists armed clashes, disturbances in the cities and changes in government policy that have come to the attention of the personnel in Kabul, in a sense offering a pool report for the news agencies and correspondents who are barred from covering the events in person.

The diplomats in Kabul, however, are severely hampered in gathering information. They are not allowed to leave the capital, and the embassies are subjected to round-the-clock surveillance. Any Afghan who contacts a diplomat runs the immediate risk of being picked up by the internal security service. Kabul residents -- whom I interviewed during the weeks that I stayed in the area around the capital this year and last year -- all said that it was not sensible to be seen near a Western embassy.

"It is the quickest way of getting yourself arrested," one resident said. Informed sources say that some embassies are worried about the security of their own employes in Kabul.

Diplomats who have served in Kabul acknowledge that they found it nearly impossible to speak to Afghans except for the ones employed by the embassy and, in one envoy's words, "when you're doing the shopping."

The Soviets and the government in Kabul also have taken care to minimize the number of experienced "Afghan hands" posted by Western governments to Afghanistan. Earlier this year, the State Department proposed to send Archer Blood, at the time stationed in New Delhi, to replace Hawthorne Mills as the new charge d'affaires of the embassy.

Accreditation for Blood was refused by the Babrak government, however, and it appeared likely that the refusal was because Blood had twice served in Kabul before. The acting charge, however, Charles Dunbar, served in Kabul from 1967-1970 and also has worked in neighboring Iran.

Given the restrictions imposed on the diplomats, they seem to do well to produce a report at all. The information collected about the situation in Kabul appears generally to be fairly accurate. Here the diplomats are in a position to observe some events personally and to talk to at least one or two residents.

But, as I discovered on several occasions while inside Afghanistan, much of the information reported about what is happening outside the capital is inaccurate. I noticed that people from Kabul were much less critical than persons in the countryside of the accuracy of reporting by the British Broadcasting Corp. -- whose Persian language service carried the faulty report of the "attack" on the air base.

The lack of reliable news about events in the countryside was brought home to me with a vengeance during my trip inside the country last year. In the middle of July, the Soviets launched one of their major offensives against the insurgents holding the Paghman region 12 miles northwest of Kabul. The fighting lasted three days, and the guerrillas held out despite being severely tested. Casualties were higher than ever, but the insurgents were proud of having forced the Soviets to withdraw in the end.

A few days after the attack, I was sitting with a group of eight or nine insurgents when a dispatch from New Delhi, again broadcast on the BBC, spoke of the offensive and said that all of the guerrillas had fled.

The reaction of the guerrillas was violent. One of the insurgents, whose brother had been killed in the fighting, stood up in a complete rage. Knowing that I had filed dispatches for the BBC, he assumed that the report had been mine and lunged across the room brandishing a brand-new bayonet.

Luckily, others intervened and forced him back, but again the dispatch had been blatantly incorrect. The same report picked up by the BBC was printed in hundreds of newspapers all over the world.

Privately, some diplomats in Islamabad admit that they feel the briefings in their present form are something of a farce.

"It is not the fault of the people in Kabul," said one envoy. "They're being forced to come up with as much hard news as possible -- news that will get published. But it's a vicious, spiraling circle -- the stories have to be better and better."

Despite this sense of unease, the briefings are unlikely to be halted. "That might just give Moscow the idea that we are easing up, and that's of course the last thing we want to do," the diplomat said.