IRAN has played an instrumental role in the recent release of two Western hostages in Lebanon and in the gathering momentum toward a comprehensive hostage exchange, according to Iranian diplomats and former officials.The move - the culmination of several years of effort, these sources say - is a carefully calculated bid by Iran to reposition itself as a responsible regional power in order to gain access to major international financial help and remove an obstacle to restored relations with the United States. Another factor in the timing, says a source who keeps in close touch with Iranian politics, was the tightening Syrian control over Lebanon. Syria, seeking its own rapprochement with the West, was increasing its house-to-house searches; it was possible that hostages might have been found and freed without any benefit gained for the captors. If Iran played a key role in a release, it would gain credit for having salvaged a figleaf of political capital for the Lebanese Shiite groups holding the hostages. As UN Secretary-General Javier Perez de Cuellar met with an Israeli envoy at press time yesterday, expectations persisted that the first phase of a comprehensive exchange could take place soon. Israel was reportedly considering a release of some of its Lebanese and Palestinian captives over the weekend if it receives concrete information on the status of its servicemen missing in Lebanon. Israeli action would be followed by a broader exchange. Despite the Islamic Jihad letter delivered by released British hostage John McCarthy to the secretary-general on Sunday, calling for the freedom of all hostages in Europe and the Middle East, a deal is not expected to include two German hostages. The Germans apparently are held by relatives of two Lebanese brothers, Muhammed Ali and Abbas Ali Hamadei, who are in German prisons for involvement in the 1985 hijacking of a TWA airliner and kidnappings of German citizens, respectively. "I don't think the deal would fall apart without them," says a knowledgeable source. "The issue of the German hostages apparently must be resolved separately, directly with the Hamadei family." The UN secretary-general has been involved in the hostage issue for about a year - most intensively in the past few months, an Iranian diplomat indicated. Iran sought to involve the UN to find a reliable go-between with the United States, and as a prelude for UN leadership in resolving oustanding issues related to the Iran-Iraq war, says former Iranian Ambassador to the UN Mohammad Jaafar Mahallati. Iran's charge d'affaires at the UN, Javad Zarif, said in a televised interview Monday that "what you have witnessed in the past few days has been the result of a very long process of our work along with the work of others to bring about this release." In a Monitor interview Tuesday, Dr. Zarif said, "I think the Americans are putting on pressure. But others are, too - and the Americans could do much more." The British, he says, are trying very hard: "The fact that Iran and [Britain] have relations has made contacts much easier." But, he adds, there has been no movement on relations with the US. "We believe the US continues its hostile policy toward Iran. Recently, it prevented the sale of civilian passenger aircraft from Britain to Iran, because some of the parts and the engines were American-made." Though it has not been stated publicly, there is an expectation on Iran's part of reciprocation. "President Rafsanjani is looking forward to establishing relations with all Western countries in a more speedy way, since his reconstruction programs need substantial financing....A few weeks ago, they encouraged a UN representative to go to Iran to make an assessment of the war damages. This is a UN window, or door, through which Iran can establish financial relations with the major industrial countries," says Mr. Mahallati. Tehran radio reported that Iran's Oil Minister Gholam Reza Aqazadeh announced Saturday that German and Italian banks will lend Iran $856 million to help finance petrochemical projects. These are believed to be the first foreign loans accepted since the 1979 revolution in Iran. With regard to the Iran-Iraq war, aspects of UN Resolution 598 have still not been implemented. Of particular concern to Iran is international help in reconstruction and UN involvement in setting up a system of regional security. Iran does not want to be on the sidelines while arrangements are made to pay compensation for damages resulting from Iraq's invasion and seven-month occupation of Kuwait. The devastation inflicted during the Iran-Iraq war was on a much larger order of magnitude: Iranian estimates of their losses range from $350 billion to $1 trillion.