Brussels — High-level observers contacted by this correspondent in both Iran and Iraq are becoming increasingly worried about the Gulf war's final outcome. ''The situation in the Gulf area is worsening every day,'' a senior West European diplomat says.
Each side in the 31/2-year war is trying to outmaneuver the other.
The Iranians continue their huge buildup of manpower along their border with Iraq. Their strategy, as described by Western military experts in Tehran, is to stretch these regular and irregular forces along the full length of the 700-mile border in an attempt to compel Iraq to thin out its own defenses.
The Iraqis, in increasingly desperate efforts to counter this Iranian strategy and to regain the oil-rich Majnoon Islands captured in February by Iran , have resorted to two apparent strategies:
* They have announced that they have started to use their French-made Super Etendard jets and Exocet missiles against ships in the Gulf. These missiles are the same kind as those used effectively by Argentina against the British during the Falklands war. The Iraqis say they destroyed two oil tankers heading toward Iran's oil terminal on Kharg Island. Lloyd's of London confirmed that a Greek tanker, the Filikon I, was hit but not sunk last week.
* In addition, accusations that the Iraqis are using chemical weapons have multiplied. Iraq denies employing any such nerve or mustard gas, but a United Nations investigation team confirmed that chemical weapons had been used in the war. And doctors in Europe, where some Iranian casualties have been treated, confirmed that the soldiers were suffering from toxic poisoning.
Such a superior weapon system as the Super Etendard, it was speculated, would dramatically shift the balance of force in Iraq's favor if Iraq decided to use it. Regardless of whether Iraq actually used the Etendards, such a shift of balance has not happened.
The second ship Iraq claimed to have hit did sink on the same day in the same area as the Greek tanker. But the ship, a South Korean supply boat, was apparently not hit by a missile. Its owner says it capsized after an accidental explosion destroyed one of its engines.
Saturday evening a Tehran radio commentator ridiculed the Iraqis, saying, ''Iraqi pilots are not able to fly sophisticated aircrafts.''
Along the war front, which stretches from the Turkish border to the Gulf, Iranian officials repeat that more than a half million fighters are now deployed. The officials say recruiting centers in Iran are overwhelmed by thousands of volunteers wanting to go to the front.
Western military experts contacted in Tehran confirm these allegations. They say Iran is trying to force Iraq to spread its forces thin along the massive front. A European diplomat in Tehran, for example, says Iran may launch an offensive on the northern part of the front to force Iraq to send forces there.
On the southern front, Iran appears to be fortifying its position on the oil-rich Majnoon Islands, which lie six miles east of the Tigris River. An eight-mile floating bridge, made of polystyrene wrapped in sheet metal, now links the islands to the Iran-Iraq border. Western intelligence sources say the Iranians are building a huge dam along the pontoon bridge. This dam should be less vulnerable to air attacks and should accommodate heavy armored vehicles.
Iranian fighters say an Iranian amphibious force of about 350 men took the islands on Feb. 22. An Iranian revolutionary guard, who is being treated in a Belgian hospital for chemical poisoning, said the Iraqis launched 10 unsuccessful counteroffensives before dropping canisters of toxic gas on the islands.
Photographs taken by a British cameraman on the islands show very few regular soldiers. Some of the fighters appear rather old. Others are in their early teens.
''Our next move will be to occupy the Basra-Baghdad Highway,'' an official in Tehran said. He added that Iranian fighters reached the highway in February but ''decided to retreat to more secure positions to defend the Majnoons.''
Western diplomats in Tehran say the Iranians might try to advance soon on the strategic road that links the Majnoons to the Baghdad-Basra Highway. But Iranians themselves recognize that their fighters will find it difficult to stay on the very flat highway if they do not bring in antiaircraft artillery and bulldozers to build strongholds.
By cutting the Baghdad-Basra Highway between the towns of Qurnah and Uzayr, the Iranians would separate Iraq's third and fourth Army corps. But Basra itself would not be under siege. West of the Euphrates River another road and a railway link Basra to Baghdad, making it extremely difficult to block all passage between the two cities.
At the United Nations, Iran was disappointed by a Security Council declaration Friday condemning the use of chemical weapons in the war. Iran had hoped for a formal resolution condemning Iraq.
Iran's UN delegate Said Rajaie Khorassani said: ''It's a pity that because of internal reasons the Security Council couldn't do a serious job on this issue.''
Since the war began in September 1980, the Iranian government has reproached the Security Council for not denouncing Iraq as the aggressor. Iran has rejected several Security Council resolutions calling for a cease-fire.
Iran's parliamentary speaker, Hojatolislam Hashemi Rafsanjani, has also criticized UN Secretary-General Javier Perez de Cuellar for waiting several months before dispatching an investigation team to Tehran. The first Iranian soldiers wounded by toxic gas were shown to foreign reporters last Aug. 23.
Four UN toxicologists arrived in Tehran on March 13, a few days after European scientists said that wounded Iranians they had examined had been intoxicated by gas. On the basis of the UN report, Iranian Foreign Minister Ali Akbar Velayati asked members of the nonaligned movement and the Islamic Conference to condemn Iraq.
Iranian diplomats in Europe are also said to be trying to obtain a declaration from the European Community on chemical weapons. But it is unlikely that EC countries will agree to condemn Iraq even implicitly without an accompanying call for a cease-fire.
A European diplomat says: ''I trust the United States State Department when it says Iraq is using chemical weapons, but on a purely legal point of view I don't have any evidence that the gas-loaded bombs examined by United Nations experts had effectively been dropped by Iraqi aircrafts.''
The US announced March 30 the imposition of new restrictions on the sale of five chemical compounds to Iraq, as well as to Iran.
An Iranian official who toured Europe last week repeated that Iran would not negotiate with Iraq before the downfall of President Saddam Hussein. ''If necessary we'll go up to Baghdad,'' he said.
A source contacted in Tehran repeated Iran's ultimate aim of establishing an Islamic Republic in Iraq. ''Iraqi opponents in Iran could form the backbone of this new regime,'' the source said.
But the source conceded that those exiled opponents lacked support among Iraq's Sunni Muslim community.
''Anyway,'' said a young Islamic militant in Brussels, ''Baghdad is only a stage on our way to Jerusalem.''