Iranian oil production sagged seriously today as workers struck in response to a call from Shah Mohammad Reza Pahlavi's archenemy to deprive the monarch's embattled government of its major source of income.

The strike, which showed every sign of spreading, was yet another indication of the growing confrontation between the shah and Ayatollah Ruhollah Khomeini, the Paris-based Shiite Moslem leader dedicated to his overthrow.

It was the third walkout of oil workers this fall and came less than a week after production had approached normal for the first time since a serious strike last month. Described as purely political by oil specialists, the new walkout represented the opposition's major economic offensive during Moharram, the Moslem month of mourning, and paralleled new street demonstrations in the capital.

The strike began Sunday in offshore production and spread today to the Ahwaz and Marun fields in Khuzestan Province.

Spokesmen for the National Iranian Oil Co. reported that production slumped from just under 6 million barrels Saturday to 5.5 million barrels Sunday. Production today declined from a daily rate of 4.4 million barrels in the morning to 3.8 million barrels by midafternoon.

Production, which had been averaging 6.1 million barrels a day in late summer, technically could reach a daily rate of 6.5 million barrels, according to specialists.

Iran, normally second only to Saudi Arabia in world oil exports, lost an estimated $1.5 billion in the month-long strike that ended Nov. 23. Specialists calculate that Iran loses roughly $12.5 million daily for every million barrels of lost production.

Losses on such a scale are major blows to the government despite its foreign exchange reserves of more than $10 billion. Symptomatic of a sudden change of mood in world money markets was Iran's inability to find takers for a large loan in October, a mammoth humiliation for a government that had been able to command unquestioned credit abroad throughout most of the nearly year-long crisis.

As was true in the last strike, oil workers seemed to be following Khomeini's instructions to produce oil for the domestic market only.

Specialists reported, however, that of Iran's five refineries only a small unit at Kermanshah in western Iran was operating to full capacity. The world's biggest refinery at Abadan, reported strike action in the offing, although production today remained near normal.

The Tehran refinery limped along at 50 percent capacity and Tabriz. which worked throughout the earlier work stoppages, went on strike today. The Shiraz refinery has been closed for more than a month.

So far, the main effect of the strike here has been a scarcity of bottled gas used for heating and cooking. All six natural gas plants also were shut down today.

If the oil strike does spread, the giant Aghajari and Gachsarn fields are the mostly likely to be hit next.

The present strike apparently is open-ended, Specialists do not expect it to end in any event before Dec. 12. This is the day after Ashura, the anniversary of the death of Hossein, the prophet Mohammed's grandson and founder of the Shiite sect to which more than 90 percent of Iran's 35 million residents belong.

Khomeini has called for a special show of opposition to the shah's military government on that day. In an effort to avoid street violence, the government has banned religious processions that traditionally mark the holy day.

The political nature of the strike was underlined by the handsome 40 percent increase in pay and fringe benefits won by oil workers last month as their price for dropping political demands.

Informed sources reported a new wave of arrests in Khuzestan among suspected strike leaders. The military authorities previously had been releasing workers detained during the earlier strike.