A series of unexplained pipeline explosions in Iran's oil-producing province of Khuzestan have shut down exports from the world's biggest oil refinery at Abadan, industry sources said today.

The cause of the initial blast, which occurred Saturday, has not been established. But authorities are not ruling out sabotage, and tighter security measures are already being enforced.

Abadan's local revolutionary committee blamed the explosions on saboteurs, while a provincial offical said they were caused by poor pipeline maintenance.

The explosions had no immediate effect on Iran's most vital oil industry installations -- those handling the crude oil exports which earn most of the country's foreign exchange and are in strong demand by oil-short consuming nations. Exports of refined oil products account for a relatively small amount of Iran's oil income.

The explosions damaged eight or nine pipelines carrying oil products from Abadan refinery to the nearby port terminal of Bandar Mahshahr. A pipeline carrying crude oil from the big Aghajari oilfield to Abadan refinery was also damaged by the explosions, and the refinery is now said to be operating on its own stocks of crude.

In the extreme summer heat of Khuzestan Province, the bursting of a single pipeline could have triggered all the explosions, oil industry sources said.

The explosions came at a time of widespread political unrest in the province because of agitation by autonomy-seeking Iranian Arabs. A month ago they fought fierce gunbattles with the Persian community in the port city of Khorramshahr. As recently as Friday, clashes erupted between mainly Arab, antigovernment demonstrators and rival progovernment groups in the city of Ahwaz in the heart of the oil fields.

Substantial quantities of arms reportedly have been smuggled into the province, where authorities fear the resumption of large-scale intercommunal violence.

There are also signs of discontent among oil industry workers. National Iranian Oil Company management sources deny any serious labor difficulties in the oil fields.

However, there is serious concern over the vulnerability to sabotage of the network of pipelines crisscrossing the province as well as other oil field installations.

In the past, Iranian oil company sources say, the question was never given much consideration. Now armed patrols are to begin checking along pipelines, reinforcing the armed guards already positioned at key production and refining facilities.

The extent or cost of the damage from yesterday's explosions is not yet known. Teams and equipment were dispatched to the scene of the blast only this morning as firemen began to gain control of a blaze that the explosions set off.

The effect on the industry is being played down by oil company management.

In an unrelated oil industry development, Iran's finance minister, Ali Ardalan, today said Iran would in the future accept payment for oil in currencies other than the dollar.

Ardalan's statement seems to have taken management of both the oil company and the Central Bank completely by surprise. Top officials at the Central Bank, responsible for Iran's foreign exchange dealings and policy warned that such a move could hurt Iranian revenues.

The confusion surrounding Ardalan's statement was seen here as further exemplifying a complete lack of coordination among Iranian government bdies on economic issues, a failing that has already become apparent in the handling of the nationalization rrogram.

Meanwhile Ayatollah Ruhollah Khomeini has spoken out strongly on the need for unity and his concern over the number of different political parties and factions that have emerged in the country since the revolution.

"Today we are afraid of our friends when yesterday it was the enemy," he warned. "Thses friends bring up certain issues which will result in the destruction of our ideology."

As his speech was being broadcast to the nation yesterday evening, further evidence of the dangerous rifts in the country arose with the assassination of a prominent bazaar merchant, Taghi Haj Tarkhani, outside his home in Tehran.

Leaflets dropped at the scene of the shooting said it was the work of Forqan, a shadowy organization that claimed responsibility for two earlier assassinations and an unsuccessful attempt on the life of a prominent religious leader.

Tarkhani, a longtime opponent of the shah, is said to have played a major part in raising funds for Ayatollah Khomeini before his return to Iran from exile last February.