Soviet forces were reported to have clashed yesterday with the Afghan Army troops that the Russians say they came to Kabul to support, according to accounts reaching Pakistan.

In a separate report, correspondents in Kabul for Reuter news agency said that they heard the firing of heavy guns in the airport area but that Afghan authorities would not allow them to go there.

The reported clash came shortly after the Tass news agency in Moscow said that Afghanistan was expelling all American correspondents for "gross interference in the affairs of a sovereign state."

The announcement of the ouster, reported from Kabul, was made by the ruling Afghan Revolutionary Council, headed by President Babrak Karmal.

The council was critical of American news accounts of the Soviet invasion of Afghanistan and installation of a pro-Moscow government headed by Babrak. It said the U.S. reporters had been writing "inventions and insinuations, each one more clumsy than the one before. Their goal is to increase tension in our country, and disrupt the normal life of the Afghan people."

It singled out Washington Post correspondent William Branigin, James P. Sterba of The New York Times, James Dorsey of The Christian Science Monitor and the correspondents of the U.S. television networks.

The expulsion order goes into effect Friday, but the correspondents were held at their Kabul hotel by Afghan authorities yesterday.

Washington Post correspondent Stuart Auerbach reported from Islamabad, Pakistan that Pakistani President Mohanned Zia ul-haq confirmed reports of the Soviet-Afghan clashes.

In an interview with American reporters, Zia called the fighting "an attempt by regular Afghan forces to show contempt for the military occupiers." a

Initial reports indicated that 30 to 50 American reporters and cameramen were in Afghanistan. Non-Americans working for U.S. news agencies apparently are not affected.

Afghan authorities detained the Americans Wednesday night after they refused to register with the Interior Ministry, diplomatic sources reported.

A State Department spokesman said the expulsion violated "basic norms and international behavior." It followed the expulsion of U.S. journalists in Iran earlier this week.

"It's reprehensible and yet another indication of the absolute contempt for human rights that exists there," he said.

Afghanistan was reluctant to let Western journalists into the country after the Dec. 27 coup and for the first week turned away reporters when they flew into Kabul airport.

Although it could not be immediately confirmed if the reported fighting in Kabul came from the airport or a nearby location, it was known that Soviet troops have formed a heavy fortification at the airport since coming to the capital city.

The extent and nature of the fighting was also unknown, but a Soviet civil aircraft took off for Moscow soon after the firing started.

Soviet troops have formed a defensive ring around the city with batteries of medium-ranged howitzers and it seemed likely these were in operation during the fighting, Reuter reported.

The British news agency also said an aircraft was seen burning Wednesday for several hours to the north of the runway at the airport, where hundreds of Soviet troops and tanks are stationed.

Auerbach reported from Islamabad that diplomatic sources said aircraft were flying over the scene of the firing and that it appeared that some of the shooting was coming from the planes.

Although he said he had few details, Zia said the fighting was at the hilltop Bala Hissar fortress and at the airport. He called the clashes heavy. He suggested that the fighting could be between a Soviet airborne division in Kabul and elements of the Afghan Army tank corps.

The State Department said it had no confirmation of the fighting.

The reliability of the Afghan Army has been an issue since the Soviet troops entered the mountainous Southwest Asian country, U.S. sources had questioned whether the Afghans, known for their fierce independence, would accept the Soviet forces. But the Afghan Army, estimated at 80,000 to 90,000 a year ago and falling to about 10,000 to 15,000 before the coup, is outnumbered by the estimated 85,000-to-100,000 well-trained and equipped Soviet forces in Afghanistan.

Immediately after the invasion Soviet troops were visible in Kabul, but soon after the city was secured they were removed to garrisons on the city's fringes. They were believed to have aided Afghan troops in the countryside fighting rebels who are opposed to the Marxist government out of concern for their own Islamic traditions.

The Soviets, who have drawn world-wide opposition to their invasion, said they were invited into Afghanistan by the new government to help put down insurrections encouraged by outside forces including China and the United States.

The almost total lack of communications with Kabul made it impossible to get first-hand verification of events there. Afghanistan exercises rigorous censorship and does not permit journalists to telephone or telex reports out of the country that mention the Soviet presence. Many of the Western journalists' news reports and much of their film have been hand-carried to other countries.

Other Soviet naval vessels are already in the Indian Ocean. Since the onset of the crisis over the seizure of the U.S. Embassy in Tehran, the United States has dispatched about 20 ships to the Indian Ocean-Arabian Sea area near Iran.