The ethnic rivals in this desert outpost faintained an easy peace for decades, ignoring their religious and linguistic differences and subsisting on smuggling and date farming.

Then the revolution came and changed it all.

Since an Islamic-led movement overthrew the shah last February, the truce has ended in the southeast province of Baluchistan-Sistan. It was replaced by a bitter communal war that involves Iran's central government as much as the two sparring ethnic groups.

In the past few days, traditionally submerged hostilities between the Baluchi and Sistani peoples have exploded into a bloody shooting spree that left 12 dead and 80 wounded and forced Tehran to send troops and tanks to restore order in the provincial capital.

The sporadic sniping and open street skirmishes transformed this simple town of mud houses and narrow, unpaved roads into an armed camp with masked gunmen on rooftops, deserted streets and frightened residents. c

The regional violence also dealt a significant political blow to the regime of Ayatollah Ruhollah Khomeini, which is trying to exert central control throughout Iran despite persistent provincial calls for autonomy.

What makes the difference in Baluchistan-Sistan so intriguing is that the revolution that was opposed to unite the nation under the banner of Islam actually sparked the current uprising in the traditionally quiet province.

The dominant Baluchis have demanded some form of self-rule, called for the dismissial of the Khomeini-appointed governor general, and shackled the feared revolutionary militia of Khomeini that polices the province.

"What we want is for the outside officials to be gone and for them to have some respect for our religious customs and our regional customs." said Mowlavi Abdol-Aziz, the Baluchi spiritual leader.

"If there is no realism," warned the turbaned cleric, "we will have more bloodshed."

Baluchistan-Sistan may have been the last place government officials would have expected warnings of that sort. An arid, mountainous chunk of land straddling the Pakistan and Afghanistan borders, it has long been one of Iran's least politicized provinces.

When most of the nation was rejoicing at the shah's overthrow and destroying any remnant of his rule, the people of Sistan-Baluchistan let a statue of the deposed monarch remain standing in the town square here until soldiers removed it two days after the revolution.

The province also is far removed from the modernization and sophisticated oil-based economy of Iran. Few homes have running water or heat. Central Zahedan is a medieval throwback, with veiled women carrying large plates of fresh meat on their heads and men pushing carts of dry goods or shouldering heavy furniture.

In such a simple society, survival has long dominated the life of the province's 600,000 people, superseding the kind of ethnic warfare that could interrupt the traditional work of both groups -- the Sistanis as date farmers and bazaar shopkeepers and the Baluchis as nomadic shepherds and smugglers who bring duty-free cigarettes and radios across the Pakistani border and sell them at a "smugglers' market" in Zahedan.

But several months ago, the revolution that virtually passed by Baluchistan-Sistan last February began slowly reaching the remote province 1,000 miles from Tehran, jarring the delicate political balance and turning one ethnic group against the other.

Ironically, it was Islam, the spiritual force behind the revolution, that tipped the scales.

Although almost everybody in the province is a Moslem, only the Sistanis are of the same Shiite sect as Khomeini and the ruling clergy. The Baluchis, who make up three-quarters of the population here, are adherents of Sunni Islam, the orthodox branch that is dominant worldwide but a minority in Iran.

The Baluchis are a proud mountain-dwelling people who speak their own language and dress in colorful baggy trousers, long mandarin-collar shirts and spangled vests.

They were angered when Khomeini appointed a Shiite teacher from another province to serve as provincial governor general, and they were further angered because they felt that the governor general was placing relatives and friends in key jobs such as head of the local radio and television station.

Then there was the local election in September which they believed was rigged by Khomeini's government, and the national referendum earlier this month designated Shiism as the official religion in street demonstrations.

But it took Khomeini's Revolutionary Guards to call the Baluchis to arms.

The guards, a trigger-happy group of Shiite youths enlisted from outside the province to help keep order within, decided to disarm the population, going door to door at Baluchi homes, making searches without warrants and even frisking Baluchi women, according to Baluchi leaders.

When weapons confiscated from the Baluchis wound up in the hands of local Sistanis, the Baluchis began to sense a conspiracy of Shiites backed by Khomeini's central government.

"There are a lot of people who are using this revolution for their own benefit," asserted Abdol-Aziz.

The Sistanis, an agarian people who speak Persian, the same language spoken in Tehran and the dominant national tongue in Iran -- play down their ties to the Shiite officials sent here by Khomeini and deny that they are forming alliances with the outsiders to overwhelm the Baluchis.

Ayatollah Mohammed Kafami, the 72-year-old Sistani leader who hobbles about town with the aid of a carved black walking stick, insisted that "foreign elements" were to blame for the recent violence, not the central government representatives.

"We've always lived together and we haven't had any trouble," Kafami said in a mosque interview. "American and communist agents have started to shoot at us. This drives us apart.

A similar view is expressed by Governor General Habib Jaririe, an excitable man who hails from the city of Shiraz hundreds of miles away and assumes no blame for currrent disturbances between Sistanis and Baluchis.

Claiming he shows no favoritism to Sistanis because they are fellow Shiites, he said that he has tried to break down barriers among the people of the province. In pursuit of that goal, he said, he has erected a concrete wall cutting the governor's office in half to make it less intimidating to the average citizen and plans to convert the ornate governor's mansion into a public hospital.

When a group of Baluchis held him hostage in a government office for 17 hours last month to protest his policies, Jarrie said, he was happy to cooperate to lessen the distance between governor and governed.

But since it became clear last weekend that this one-time Shiite teacher and activist was the source of many Baluchi complaints -- the government office walls were covered with the slogan "death to the outside governor" -- Jaririe has come under pressure to resign.

During the crisis, Jaririe met frequently with Khomeini's regional trouble-shooter, Ibrahim Yazdi, who has been here since Thursday to held find a peaceful solution to provincial troubles.