Soviet troops have launched their largest land and air offensive since invading Afghanistan in late December, apparently to crush a revolt in an Afghan Army division, according to Western diplomatic reports reaching here today.

One report said Soviet helicopter gunships, MiG fighters and troop transport helicopters have filled the skies over the Afghan capital of Kabul every day since Friday. A report from a second Western area specialist called the Soviet air movements "the heaviest helicopter activity seen to date" and said that "it must represent a major action."

The reports came from diplomatic missions that often differ in their analysis of events in Afghanistan. The missions refused to be specifically indentified as a condition for giving their information to reporters.

Both agreed today that the helicopters and MiG fighters were heading southwest from Kabul toward Ghazni, where there were persistent reports that the Afghan Army's heavily armed 14th Armored Division had mutinied.

There were also reports that the mutiny had spread to other Afghan Army units in the nearby garrison at Maidan Shahr. One source in Kabul told diplomats that Afghans from the garrison have besieged 200 Soviet tanks. t

In addition, heavy fighting was reported Saturday night in the residential area of Koti Sanghi in southwestern Kabul. According to the diplomatic reports, the fighting lasted 45 minutes to an hour, during which flares and tracer shells could clearly be seen.

There was no indication of what the fighting was about.

A bloody feud between the two factions of the ruling Marxist People's Democratic Party of Afghanistan, however, was reported to be continuing in Kabul and throughout the country.

This feud was blamed for the mutiny of the 14th Armored Division, one of the strongest among the decimated Afghan Army. It is equipped with tanks, artillery, anti-aircraft guns and possibly surface-to-air missiles, all of which would be useful to Moslem rebels who have been battling both the Soviets and the government.

According to a nondiplomatic traveler who reached here this weekend, the mutiny started when the Soviet-installed government of Babrak Karmal tried to replace the 14th Division commander, a member of the Khalq (masses) wing of the ruling party, with an officer who belongs to the rival Parcham (banner) faction.

Babrak is a member of the Poarcham faction. The Khalq wing, which makes up two-thirds of the party membership and 80-percent of the military officer corps supported two former Marxist predsidents, Nur Mohammed Taraki and Hafizullah Amin.

Diplomats said indications are that the feud is intensifying despite assurances of unity at a party Central Committee meeting last week.

Kabul is filled with rumors both of the arrests by the Babrak government of top Khalq leaders and of the assassinations by Khalq supporters of key Parcham members. The government, said one diplomat, is finding it hard to refute the various allegations.

An area specialist said the reports of Afghan Army revolts gained credibility because of the high level of Soviet helicopter activity. He called the revolts "the greastest challenge" the Soviets have faced since they invaded Afghanistan in December and installed Babrak as president.

From all appearances, according to the separate diplomatic reports, the Soviets are determined to crush the revolt.

On Friday, for example, an unusually large formation of 28 heavily armed M124 helicopter gunships, the most effective Soviet weapon against the Afghan rebels, was seen heading toward Ghazni from Kabul. They returned to Kabul with signs of having fired all their ammunition, a diplomat reported.

Moreover, several large convoys of tracked armored vehicles and troop trucks have been seen leaving Kabul and heading for the Ghazni area.

Several sources in Kabul have told diplomats that there is heavy fighting in Ghazni and Wardak provinces in eastern Afghanistan southwest of Kabul. The fighting was reported to stretch down to the city of Kandahar, the country's second largest, in the southeastern corner of Afghanistan.

There were also reports of fighting in areas north of Kabul, especially Charikar just 30 miles from the capital in Parwan Province.

Diplomats reported that the Soviets have set up strong roadblocks on all major highways leading out of Kabul.

At one key junction on the way to the town of Paghman, diplomats counted four self-propelled .122mm guns, four BMP armored cars, two BMD light tanks and two BRDM armored scout ears. Many of those light, mobile armored vehicles have been brought into Afghanistan in the past month to replace heavier, more cumbersome weapons unsuited for fighting in the country's rugged terrain.

One analyst noted that the Soviet armor is positioned to repel attacks from all directions -- not just ones coming from outside Kabul.

Afghan police and Loyal Army forces, backed by two Soviet-made T34 tanks and armored personnel carriers, were reported to be searching vehicles on that road trying to enter Kabul.

By all indications, the Babrak government has been trying to quiet the rumors sweeping through Kabul about intraparty feuding.

According to the diplomatic reports, the government has been encouraging high officials who belong to the Khalq faction to refute rumors of their arrest by appearing in public. Among those Khalq partisans who suddenly began surfacing were Interior Minister Said Mohammed Gulabzoi, Central Committee member Saleh Mohammed Zeary and Revolutionary Council member Nur Ahmad Nur.

Education Minister Anahita Ratezbad, a Parcham member who is close to Babrak and was rumored to have been assassinated last week, also made a public appearance over the weekend.

The attempted assassination of Kadar Mal, the chief editor of Bakhtar, the government news agency, was reliably reported by diplomats here.