Iran is hurrying plans to build a 200-mile twin pipeline that would enable it to transport its oil farther south in the Persian Gulf, out of range of Iraqi planes that have been attacking Iran's main oil terminal at Kharg Island.

The pipeline would make the six-year-old gulf war free of any substantial threat to oil shipments from the region.

Iraq, which was exporting about 800,000 barrels a day until September, has increased its exports to 1.5 million barrels using newly built pipelines carrying oil out through Saudi Arabia and Turkey. The sections of those pipelines that are in Iraq are beyond the range of Iranian planes.

Completion of Iran's proposed new pipeline would assure both countries of ample oil export revenues to purchase the arms needed to continue their war of attrition.

According to oil shipping sources in Washington and London, the National Iranian Oil Co. sent terse messages to 11 Asian and European companies in mid-October inviting them to bid on a twin pipeline from Gurreh, the underground pumping station for Kharg Island, to Asaluyeh.

The oil would be loaded on tankers from floating terminals or large crude carriers moored at Bushehr, about 50 miles south of Kharg, and Asaluyeh.

A spokesman for the Italian Saipem company, based in Milan, confirmed that his company received the Iranian invitation and said that the pipeline would be a relatively large 42 inches in diameter and that the "Iranians are in a rush to finish it as soon as they can."

The spokesman, who asked not to be identified, said, "the invitation came to us more than a month ago. It asked us to present our offers by Nov. 20 and [said] that we should be getting a response from the Iranians in early December."

He said that his company had not received a response yet and that he knew of no other company that had received an answer.

"The last we heard from them was that they will make their decision by late December or early next year," he said.

Two British companies, Costain Process Engineering and Construction Co. and Stone and Webster Engineering Co., a subcontractor for South Korea's Daelim Industrial Co., confirmed having received the invitation telex and sending offers to the Iranian government.

Iranian newspapers reported in November that the government was negotiating the purchase of mobile buoys with the Turkish and West German governments, although it neither revealed the purpose of the purchases nor mentioned pipeline plans.

An economist at the World Bank in Washington who follows developments related to oil shipments from the Persian Gulf said Iran had already acquired three buoys, which would allow it to export up to 2 million barrels a day.

"Buoys are single spots on the ocean, and it is extremely hard to hit them in aerial attacks; and, given the inaccuracy that Iraqi pilots have shown in their previous attacks, it is very unlikely that such buoys would be damaged by Iraq," said the economist, who asked not to be identified.

"Even if attacked accurately, they can easily be repaired or replaced in a very short time," he said.

"Basically, what it boils down to is that once this pipeline is completed, Iranians can totally bypass the Kharg production. Although, my guess is they will probably keep it running and try to get as much as out of it as they can," he said.

Iran, in its message sent out in October, said it wished to complete the pipeline in 12 months, a deadline some of the firms invited to bid find unrealistic.

The tight timetable also would increase the cost of the project, which spokesmen for the companies say could run from $500 million to $800 million.

They said the cost would depend on construction speed, the materials used and the number of companies participating in the project.

According to the Iranian telex, the cost of the pipeline will be paid "fully or partially through oil barter," something about which bidders have expressed doubts.

"Since the Iranians are in such a rush to finish the construction of the pipeline, it will become more important for us to have some cash money in advance to begin the work with. Therefore, if Iran gives us the oil before the completion of the pipeline, that is good enough and we can consider it as cash. Otherwise, it is no good as far as we are concerned," said a spokesman for the West German company Mannesmann, another firm that received a copy of the invitation.

According to the companies contacted, the Iranians have given bidders up to seven months to complete the first 108-mile phase of the pipeline connecting Gurreh to mobile terminals at Bushehr.

That line would be a backup for exports from Kharg Island until the pipeline is completed. Through other minor storage fields, Iran then would be able to decrease considerably its reliance on Kharg.

The other half of the pipeline is to be built in five months linking Bushehr to Asaluyeh through Taheri from where, the spokesman for the Saipem company said, Iran has been building a gas pipeline to Ahvaz.

"The pipeline is a reversible gas-to-oil line, which would enable Iranians to send their gas from Taheri to Ahvaz and transfer their oil from Ahvaz to Taheri to be loaded onto tankers from there," he said.

Iran has been heavily dependent on Kharg Island to export oil, which provides more than 90 percent of its foreign currency. Last August Iraq began bombing the island and since then has claimed repeatedly to have destroyed it.

But oil shipping sources have said few attacks actually hit their targets, mainly because Iraqi pilots flew too high to be accurate.

It was reported in September that some hits seriously endangered Iran's capability to export oil from Kharg, which may have caused Iran's tight timetable for building the pipeline.