The State Department, accusing the Soviet Union of "blatant military interference" in Afghanistan, said yesterday that the Soviets carried out a 150-plane airlift of troops and field equipment into that country during the last two days.

In addition, department spokesman Hodding Carter said, "The Soviet military buildup north of the Afghan border is continuing, and we now have indications that there are the equivalent of five divisions in soviet areas adjacent to Afghanistan."

Although Carter charged that the Soviets "are crossing a new threshhold in their military deployments into Afghanistan," he said he could not estimate the number of troops involved in the airlift Tuesday and yesterday.

However, department officials said as many as 4,000 combat-equipped troops may have been involved in the new airlift. In a briefing Saturday, a senior department official, who declined to be identified, said about 1,500 Soviet combat troops had been brought into the country during the preceeding two weeks.

This infusion of combat forces, totaling about 5,500 men, according to the department's estimate, is in addition to about 3,500 Soviet military advisers who have been in Afghanistan for the past year.

Department officials also said they could not say with certainty how many troops are in the five divisions allegedly stationed on the Soviet side of the Afghan border. If these divisions are at full strength, they would total approximately 50,000 men.

The department's statement, volunteered by Carter at the beginning of his regular daily news briefing, marked a new escalation of official U.S. concern that Moscow is trying to strengthen the pro-Soviet regime of Hafizullah Amin against threats from rebel tribesmen in order to transform Afghanistan into a Soviet-dominated client state.

Afghanistan, formerly an autonomous buffer state in the eastern end of the volatile southwest Asia area that diplomats call "the arc of crisis," has moved progressively closer to the Soviet Union since the April 1978 coup that placed the present ruling group in power. The original coup leader, Nur Mohammed Taraki, was ousted by Amin three months ago.

However, as the regime has encountered increasingly bloody resistance from Islamic tribes opposed to its policies, Moscow has been engaged in a steady buildup of military support for the government, primarily through the supply of advisers and equipment.

Until now the United States, while expressing concern about this buildup, has said it has no evidence of Soviet forces engaging in actual military operations against the rebel tribesmen. Hodding Carter and other State Department officials stressed yesterday that they do not know whether the sudden infusion of Soviet combat troops into Afghanistan is a signal of an impending shift by the Soviets from the role of advisers to participants in the fighting.

These officials added that with the exception of Soviet troop movements into the satellite countries of Eastern Europe and into Cuba, Moscow's injection of combat forces into Afghanistan in such numbers is unprecedented in the postwar period.

Barring these exceptions the officials said Soviet forces have not turned up in another country in such massive strength since the Soviet incursions into Afghanistan's neighbor Iran right after World War II. At that time the Soviets were forced by American pressure to withdraw.

The officials yesterday repeated past assertions that there does not appear to be any direct link between the Soviet moves in afghanistan and the neighboring crisis between Iran and the United States. In fact the officials said some of the Soviet forces now stationed near the Afghan border apparently have been shifted from areas of the Soviet Union adjacent to Iran.

There have been suggestions that the United States, under heavy fire in parts of the Islamic world because of its confrontation with Iran, has been seeking to call attention to Moscow's military role in helping to crush what is partly a religious revolt by Afghanistan's Ilsamic tribesmen.

In his statement yesterday, Hodding Carter said: "We believe that members of the international community should condemn such blatant military interference into the internal affairs of an independent sovereign state. We are making our views known directly to the Soviets."

Asked to elaborate, he said the Soviets, in commenting on the U.S.-Iranian crisis, have warned repeatedly in recent weeks about big countries not interfering in the internal affairs of smaller nations.

He also cited the volatility of the area, and said, "The interjection of external combat troops into one nation of the region can be properly seen by others as a matter of concern for their own stability."

Both Iran and Pakistan, Afghanistan's neighbor to the east, reportedly are concerned about the increasing Soviet military presence, and some concern also has been reported in India.

But, in response to questions about whether there was any suggestion that the Soviets had invaded Afghanistan or were there in any capacity other than at the invitation of the Afghan regime, Carter said, "Why don't you address that question to the Afghanistan government?"

In private, U.S. officials said their efforts to obtain information from the Kabul authorities about the Soviet military role there have been met largely with evasions and in unwillngness even to admit the existence of the Soviet presence.

Carter said the airlift had been carried out by Soviet AN22 transports capable of carrying 175 fully equipped soldiers, and smaller AN12s, which can carry 90 men each. He added that the whereabouts of all the Soviets troops brought into the Kabul area by the airlift were not known, but that hundreds were still camped in the vicinity of the airport yesterday.