Iranian oil production slumped drastically to less than a quarter of normal output today as politically motivated opposition strikers tightened their stranglehold on embattled Shah Mohammad Reza Pahlavi's principal foreign exchange earner.

The nine-day-old strike has so badly disrupted domestic supplies of kerosene-used extensively for cooking and heating-that Iran's key oil troubleshooter, Parviz Mina, reportedly has been sent abroad to arrange imports.

Mina's trip to Kuwait and Saudi Arabia was clearly dictated by the realization that the hard-pressed shah could ill afford even greater popular discontent that a serious kerosene shortage could cause as winter approaches.

Normal production, which had crept back to 6 million barrels a day after recovering from an earlier strike, slipped to 1.3 million barrels today.

Oil officials in Khuzestan, the oil producing province in southern Iran, said their impression was that "production is not going to improve for the foreseeable future."

Each unpumped million barrels of oil represent a loss of $12.5 million and last month's long strike is estimated to have deprived the government of $1.5 billion.

The striks, called by the shah's archenemy, Paris-based Moslem religious leader Ayatollah Ruhollah Khomeini, gave some signs of spreading. Khomeini wanted production limited to home consumption needs, estimated at 625,000 barrels a day.

At a demonstration in Ahwaz Monday, a strike leader called for further cuts in production and complained that some crude was being exported to South Africa, a longstanding Iranian client.

In the past strikers have also complained about sales to Israel, which relies extensively on Iranian crude.

Thanks largely to specially trained Iranian navy technicians and European and American specialists, production in the Paris and Karanj fields was reported running at 600,000 barrels or roughly what the world's number two exporter can find to sell abroad.

Also still pumping were units in the March and Ahwaz fields.

Production for the home market is still sufficient, in theory, to meet demand. But Mina's foreign kerosene buying mission underlined the dislocations caused by spotty operations in the country's various refineries, some of which are either completely shut down or working at a reduced level.

So far, oil officials have reported no sabotage, but said they were having a "tough time" maintaing the various installations.

Despite this third oil strike this fall, government foreign exchange coffers are not immediately threatened by the new stoppage. They stand at more than $10 billion.

But the pyschological effect of repeated shutdowns in the single industry which fuels Iran's economy-at a rate of between $20 billion and $22 billion annually in better times - is regarded as further proof at home and abroad of the shah's increasingly precarious hold.