Rebelling Moslem tribesmen were reported yesterday to be battling troops of the pro-Soviet government of Afghanistan in the remote, mountainous region where the Afghan, Soviet and Iranian borders meet.

State Department officials and diplomatic sources here have received conflicting reports as to whether the ancient trading city of Herat, the fourth largest in Afghanistan, has fallen into rebel hands.

Telephone communications between Herat and Kabul, Afghanistan's capital city, a long day's journey over rough roads to the east, have been down since Thursday and the State Department said it is unclear who controls the city.

Five Americans, missionaries at the Noor Eye Hospital, are in Herat, but neither the U.S. Embassy nor their headquarters in Kabul has been able to contact them.

The government of Afghanistan has charged that the revolt is being fostered by Iran and accused the revolutionary government there of sending 4,000 troops over the border disguised as refugees returning home.

Iran denied the charges. Nonetheless, Agence France-Presse reported today from Pakistan that Afghanistan has given the Iranian consul in Herat 48 hours to leave the country. The expulsion order was handed to Iranian diplomats in Kabul, AFP quoted Radio Kabul as reporting.

Despite the Afghan government's charges against Iran, analysts here believe the rebellion is home grown -- bolstered by aid from exiled Afghan Moslem leaders in Pakistan who have called for a "jihad" (holy war) against the present government of Afghanistan, which seized power in a bloody coup last April.

The tribesmen who have been carrying the fighting near Herat traditionally have resisted central authority -- dating from the days when the British ruled the territory.

But their current battle is fueled by the pro-Soviet stance of the present government of Afghanistan.

These tribesmen are Shiite Moslems -- the same branch of the Islamic religion that dominates Iran -- and they fear that the Kabul government will not allow them to practice their religion the way they want to. "Godless Communists" is the way they describe the government of Afghani President Nur Mohammed Taraki.

Beyond that, political rivals of the Taraki government are using the religious ferment in an attempt to get themselves into power.

They have set themselves up in Pakistan, in the city of Peshawar just over the Afghan border, and are attempting to form a united front. One of the National Liberation Front, said the fighting came in response to a general call last week for an uprising against Taraki.

The fighting has spilled over into an international war of words, with the Soviets showing their concern by accusing Pakistan, Egypt, China and the West of fostering it.

Egyptian newspapers denied their country had anything to do with the uprising but said it was directly connected with Soviet ambitions in the Islamic Middle East. Pakistan's President Mohammed Zia ul-Haq traveled to Peshawar Monday to deny the charges.

Nevertheless, there is little that he can do to prevent Afghan exiles from using Pakistani territory since his government is dependent on the support of the Shiite Moslems. Holy men in Pakistan have condemned the Taraki government for using "coercion, intimidation, violence and torture" against Moslem leaders there.

A ranking Shiite leader in Iran, Ayatollah Kazem Shariatmadari, also accused the Afghan government of massacring thousands of Shiites, including 170 religious leaders. He called for Moslems throughout the world to come to the support of Afghanistan's Shiites, but observers here said his rallying cry is too recent to have influenced the fighting in western Afghanistan.