Iran has resumed pumping natural gas to the Soviet Union in another sign that the gas and oil industry is recovering its role as the country's principal foreign exchange earner capable of carrying the otherwise strained economy.

Energy specialists said today shipments through the 746-mile pipeline from southern Iranian fields to Soviet ports on the Caspian Sea began recently "at a very low rate" compared to the one billion cubic feet a day exported before last December's oil and gas strike.

The strike, which played a crucial role in ousting Shah Mohammad Reza Pahlavi, caused acute shortages this winter in the energy-poor southern Soviet republics of Armenia, Azerbaijan and Georgia.

With the pipeline, completed in 1970, Iran supplied natural gas to the Soviet Union, which in turn sold its own gas to Western Europe.

The pace of Iranian deliveries to the Soviet Union depends on oil production in the Ahwaz, Aghagari and Maroun fields of Khuzestan, which produce natural gas as a byproduct of oil. A combination of political and maintenance problems in these more restive fields is believed responsible for delaying resumption of gas exports and limiting their present levels.

Oil production, which was limited to 700,00 barrels a day for domestic consumption during the export ban from Dec. 26 to March 5, has now reached a range of 2.5 million to 3 million barrels a day.

Energy specialists and government officials are predicting that production could soon reach the revised postrevolutionary goal of between 4 million and 4.5 million barrels a day without foreign experts or sophisticated gas injection schemes.

This is still far from the 6 million barrels a day produced under the shah, which made Iran second only to Saudi Arabia as an oil exporter. But it demonstrates the gradual reassessment upward of optimum production by the revolutionary authorities.

After criticizing the wastefulness of the shah's maximum production policy that pad for Western arms and other prestige products, revolutionary authorities realize they have a certain dependency on oil revenues to keep a potentially explosive political situation under control.

Restless national minorities such as the Kurds, Turkomans and Baluchis - as well as Khuzestan's large Arab population - are demanding more central government investments as the price for cooperating with Tehran.

Government officials deny reports that 3.5 million Iraians have lost their jobs because of the revolutionary disruptions during the fall and winter. But unemployment is serious and revolutionary authorities want to avoid allowing social discontent to spill over publicly.

The temptation to subsidize food, make work and otherwise use government funds to underwrite stability is understandably attractive, observers believe, at a time when the economy is suffering from lack of discipline, shortages of spare parts and the departure of foreign experts.

The National Iranian Oil Co. is considering hiring back about 100 foreign specialists, but the Iranians have already proved they can handle operations at the present level.

Oil exports have averaged 1.2 million barrels a day. Domestic production siphons off about 700,000 barrels a day and 800,000 barrels a day are being pumped into 40-million barrels worth of storage capacity depleted during the strike and its aftermath.

In any case, bring back foreigners, although approved by Prime Minister Mehdi Bazargan, is still a politically touchy problem so soon after Iran's revoluation. Whether the government could provide sufficient security - and financial inducement - to attract many foreigners remains to be seen.

Still up in the air is Iran's relationship with the 14-company Western consortium led by British Petroleum and including a majority of American firms. Although revolutionary authorities have announced determination to end the relationship, the consortium has said nothing in public.

In general, energy specialists gave Iran's National Iranian Oil Co. credit for getting production started up again. Although Hassan Nazih, the recently appointed oil company chairman, has made no important senior management changes, the organization's upper hierarchy nevertheless is said to suffer from the same lack of decisiveness that plagues so many sectors of Iranian life in these postrevolutionary days. CAPTION: Picture, Natural gas being flared off at Iranian refinery. AP