Soviets put heat on Afghanistan.

The latest series of Soviet offensives against the strategic Panjshir Valley and other major Afghan resistance strongholds appears to be the largest in more than four years of warfare.

From the point of view of Afghanistan's long-suffering civilians, the assaults promise also to be among the most devastating.

The Soviet Army high command and Afghan government have thrown more than 20, 000 mainly Soviet troops into the Panjshir, supported by tanks, helicopter gunships, and highly maneuverable fighter-bombers. Similar operations but involving fewer men have been launched against other regions, notably Kandahar, Nangarhar, Herat, and Mazar-i-Sharif.

This new wave of ''cordon and thump'' attacks does not represent a strikingly new form of Soviet strategy. Massive ground and air operations directed against both civilian and guerrilla concentrations have characterized the Kremlin's anti-insurgent policies for the past three years.

The main new development - possibly indicating the Kremlin's growing frustration with the war - is that the Soviets have chosen to launch half a dozen such operations more or less in concert over a three-month period, thus bringing mujahideen guerrillas under heavy pressure in several areas at the same time.

In addition, there is no doubt that these assaults, particularly that against the Panjshir Valley, will further destroy Afghan villages and farms, making it even more difficult for the civilian population to survive. This time, the Soviets also are reportedly using high-level bombing, with its indiscriminate effects.

In what is perceived by the Afghan resistance as a deliberate policy of ''migratory genocide,'' the Soviets are seeking to make living conditions so harsh that most Afghans will eventually be forced to leave the country - as nearly 5 million have done so far - or accept communist tutelage.

Resistance forces and relief workers have already reported large influxes of refugees who have fled the heavy bombardments and crossed over into Pakistan. Thousands of others, many of whom fled before the fighting began, have sought shelter in nearby mountains, neighboring provinces, or in Kabul itself.

The guerrilla leadership, which is constantly appealing for outside aid, is fully aware that, lacking the support of local inhabitants, it will become increasingly difficult to pursue an effective form of antigovernment warfare.

But claims by the Kabul regime that its forces have defeated the estimated 5, 000 guerrillas of the Panjshiri commander,

Ahmed Shah Massoud, are regarded with skepticism by Western observers. The present offensive in the Panjshir, reportedly

launched April 21, is the seventh so far since the Soviet invasion of Afghanistan in December 1979. None have pacified the valley.

During the last two Panjshir assaults in May and September 1982, Red Army and Afghan troops managed to occupy most of the 70-mile-long valley floor but failed to hold out against constant guerrilla harassment.

Despite a deployment of well over 12,000 men, including specialized heliborne commandos, backed by armored vehicles, helicopter gunships, and SU-24 fighter-bombers, the Soviets eventually withdrew to the lower regions of the valley.

Afghan government garrisons left in their wake fell one after another to the guerrillas

through direct attack or defection.

Faced by a stalemate, the Soviets negotiated a temporary truce with Massoud. This came into effect in January 1983 but was terminated with the present military operation when the Panjshiris refused to renew it.

In many respects, this seventh offensive appears to be a replay of the previous two but with larger numbers involved. As before, Afghan government propaganda maintains that Massoud's ''band of bandit followers'' has been liquidated and that the people of the Panjshir, wherever they are, should return to enjoy the new peace.

There have been government-inspired reports that Massoud has been captured. But these are strongly doubted by Western diplomats in light of previous such claims.

In addition, according to resistance sources in Paris, although one government Khad (Afghan secret police) agent nearly succeeded in assassinating Massoud prior to the offensive by firing at him from a distance of 30 feet, the would-be assassin missed. Two others, also sent out on a mission to kill him, were apprehended before they could make an attempt.

Massoud's forces now appear to have adopted conventional guerrilla strategy by slipping into the mountains and then hitting the invaders from all sides. The young Panjshiri commander, who has the cooperation of mujahideen commanders outside the valley, has apparently dispatched groups of mobile guerrillas to the plains of Shomali, north of Kabul, to strike at government supply lines.

Unconfirmed reports indicate that the mujahideen have halted the Soviet advance into the Panjshir Valley and have inflicted severe casualties.

If previous Soviet attempts are any indication, the present Soviet force may succeed in securing a foothold in the valley, but only at a considerable cost. As before, mass defections by Afghan Army conscripts who fronted the attack are believed to have occurred.

The destruction of several bridges over the past few weeks will no doubt oblige the Soviets to supply their forces by air. And, unlike the 1982 offensive , this year the Panjshiri guerrillas are vastly better equipped with antiaircraft weapons and heavy machine guns.