Iran set to pipe oil through Soviet Union. Iranian-Soviet ties are on an upswing. The two countries' planned oil and gas venture could significantly alter the strategic balance in the Gulf. Related stories, Pages 2, 7, and 9.

More than a third of Iran's daily oil exports will soon pass through the Soviet Union, Iranian officials say. This is the result, they say, of an agreement negotiated by the two countries during last week's Tehran visit of Yuli Vorontsov, the Soviet first deputy minister of foreign affairs. The Iranians add that the contract, involving the conversion of an existing gas line into an oil pipeline, will be formally signed by the end of the month.

In Moscow, a Soviet ministry spokesman confirmed the projected accord and said, ``Some details remain to be finalized, but both Iran and the Soviet Union want the deal to be wrapped up.''

Western oil industrialists say such an agreement would signal a major change in Iran's oil policy - one that will have long-term strategic consequences in the region.

In the past, the national Iranian oil company had repeatedly said all crude oil exports must go through the Gulf. The company believed that exporting through terminals outside the waterway would diminish Iran's strategic importance.

A European oil company expert says the Iran-Soviet accord would have two main consequences:

Any major successful strike on Iran's terminals in the Gulf or the Indian Ocean would transform the country into a de facto Soviet satellite.

Iraqi hopes of bringing Iran to the negotiation table by disrupting its oil exports would be dashed.

Western observers in Tehran say the Soviets are trying to render both Iran and Iraq economically dependent on them, with the aim of forcing both into negotiations on the Iran-Iraq war which would be held in Moscow.

Some observers also believe the Iran-Iraq war may have entered a new phase, with the Iranians having secretly promised the Soviets to deescalate the fighting on land. Iran, they say, is striving to secure additional revenues for the reconstruction of its crippled economy.

An Iranian source close to Prime Minister Hossein Musavi says the agreement provides for an existing gas pipeline between the south of Iran and the Soviet city of Baku to be converted soon into an oil pipeline.

This pipeline was built under the imperial regime of the Shah and is known as IGAT 1. It is currently not in use, since Iran cut its gas sales to the Soviet Union in May 1980 after a price dispute, and later the Soviets refused to reopen it.

From Baku, this source says, Iran's oil will be pumped to one of the Soviet terminals on the Black Sea, where it will be sold as Iranian oil.

Iran and the Soviet Union also agreed, the source adds, on the construction of a second line - the IGAT 2 - that will feed Soviet Armenia with gas from Iran's Kangan field.

By March of next year, the source continues, Iran will complete the construction of a third pipeline that will connect its Khuzestan Province oil field to a terminal on the Indian Ocean, thus bypassing the Strait of Hormuz, the narrow entrance to the Gulf. The source refuses to say whether the Soviets will participate in building this third line.

``I wonder,'' the European expert says, ``what concession the Iranians made to the Soviets to get all this.''

But the Iranians contend the projected contract is just a commercial one. ``We'll pay a traverse toll for the oil and that's it,'' an Iranian diplomat asserts.

The Iranian diplomat insists that his country wanted to reach a similar agreement with Turkey, but ``the Turks were dragging their feet, probably because of US pressure.''

Some diplomats in Tehran and Baghdad believe the Soviet Union, which insists it wants to bring a quick end to the Iran-Iraq war, may have gotten the Iranian leadership to agree to refrain from launching any large offensive in the foreseeable future.

Indeed, Iranian officials - who only a few months ago regularly trumpeted that they would soon defeat the Iraqi Army for good - have become much more cautious. ``We'll win the war, even if it takes us 20 years,'' a Bonn-based Iranian diplomat said last week.

In a recent interview with the Tehran daily Ettelaat, parliamentary Speaker Hashemi Rafsanjani said, ``We have to take the political decision whether to launch an all-out offensive or to wage a war of attrition against Iraq.''

Mr. Rafsanjani conceded that Iran's Supreme Defense Council was divided on the issue, and added that the first alternative would require the Iranian government to devote all its energy and resources to the conduct of the war at the expense of the country's economy.

News of the Iran-Soviet oil and gas deals came amid new signs that political relations between both countries are warming up.

Iran's ambassador in Moscow, Ali Reza Nobari, said last week that Soviet officials told him, ``The Soviet Union approves of Iran's Gulf policy and sees the reflagging of Kuwaiti tankers under US flag as a violation of the UN Security Council resolution calling for a cease-fire in the Gulf war.''

The Iranians also contend the Soviets have promised them they will veto any UN resolution calling for military or economic sanctions against Iran.

Western diplomats in Moscow say the official Tass news agency has never mentioned that the last paragraph of the UN Security Council resolution passed July 20 provides that the 15 members of the Council will meet again to discuss sanctions against any belligerent who doesn't abide by the resolution.

Claude van England writes on Iran from his base in Brussels.