KUWAIT, JULY 23 -- A convoy of four U.S. warships and two Kuwaiti tankers flying the American flag crossed the halfway mark today in their tense, 500-mile passage through the Persian Gulf to Kuwait's oil loading port.

American sailors wearing helmets and orange life vests maintained a high state of alert and scanned the heat-shimmering horizon for trouble. Others manned every sort of weapon from deck-mounted machine guns to antiair and antiship missiles, as well as antimissile Gatling guns.

Pool reporters aboard the warships witnessed a vivid display of American weapons technology at work, as satellite dishes shimmied hydraulically to keep a lock on invisible communications links in space and an array of radar sensors scanned the horizon with help from airborne surveillance planes.

As the convoy steamed up the shallow and sun-drenched gulf, Iranian officials declared that the Kuwaiti petroleum exports aboard the reflagged tankers would be considered "prohibited goods" being transported in support of the Iraqi war effort. Western officials took the Iranian statement to mean that its naval forces might try to intercept future convoys or subject them to guerrilla or suicide attacks.

Rear Adm. Harold Bernsen, commander of the Navy's nine-ship Middle East Task Force, told reporters in the Pentagon's media pool, "So far, it has gone precisely the way I thought it would -- smoothly, without any confrontation on the part of Iran."

Bernsen added that the Iranian Air Force and Navy are "not strong" and said, "It would not be in their best interests to utilize their forces in a direct confrontation."

Iran's Foreign Minister Ali Akbar Velayati, in a message to U.N. Secretary General Javier Perez de Cuellar, reportedly complained that all during the seven-year-old gulf war, Kuwait has aided Iraq and has "sold oil on its behalf.

"Therefore, contrary to what U.S. officials had claimed, Kuwaiti tankers flying the U.S. flag were practically carrying oil for the aggressor Iraqi regime," Velayati said.

Kuwait and Saudi Arabia pump and export 300,000 barrels of oil a day from the neutral zone on their common border and the revenues from this oil are turned over to Iraq.

{Foreign Minister Velayati said during a visit to Bonn, however, that Tehran would refrain from attacking ships in the gulf as long as Iraq did the same, Washington Post correspondent Robert J. McCartney reported.

{Speaking at a news conference after talks with top West German officials, Velayati also rebuffed the cease-fire resolution passed by the U.N. Security Council Monday. Iran will not participate in U.N.-sponsored efforts to end the war until the world body condemns Iraq for having started the conflict, he said.}

{Iraq's Deputy Prime Minister, Tariq Aziz, tonight avoided any commitment to halt attacks on Iranian shipping, Reuter reported. Following a meeting with de Cuellar in New York, Aziz said the United States had not asked Iraq to halt attacks on ships in order to avert similar assaults by Iran.

{"We have not been asked by anybody to do that," Aziz told reporters. He said Iraq would accept a complete ceasefire, but said that Iranian troops must lay down their arms as a "prerequisite."}

Tehran Radio announced today that Iran's Revolutionary Guards will mount a series of naval maneuvers code-named Martyrdom early next month, timed to coincide with the passage through the gulf of the next U.S.-escorted convoy.

An Iranian military spokesman said the exercises "will show the world that the navy of the Revolutionary Guards can . . . crush arrogance and implement the guard corps' special methods."

Meanwhile, fighting has continued in the land war between Iran and Iraq despite the Security Council resolution. However, the resolution appears to have given a brief respite to the "tanker war" that has raged intermittently since 1984, killing scores of crewmen and damaging more than 250 ships.

Foreign diplomats in Baghdad were reported today to believe that Iraq will not reignite the tanker war, silent now for 10 days, until Perez de Cuellar has time to try to persuade Iran to come to some kind of accommodation acceptable to Iraq for ending the war.

The American convoy was expected to arrive around noon Friday at its destination off the coast of Kuwait, where the supertanker Bridgeton will tie up at Kuwait's offshore sea islands to begin crude oil loading operations that will last through the weekend.

Bridgeton, one of the largest ships in the world with a length equal to nearly four football fields, will operate a continuous shuttle between Kuwait and an anchorage outside the gulf where it will offload crude oil to smaller tankers and then return for another load.

The smaller Gas Prince will come into port Friday and tie up at Kuwait's natural gas pier for a five-day loading operation. The Gas Prince will not be involved in shuttle operations, but will take its load of natural gas to customers in the Far East.

Late reports from pool reporters aboard the U.S. naval escort flotilla described a brief, but tense encounter yesterday between the American task force and a flight of Iranian F4 fighter bombers, which scrambled from an air base near Bandar Abbas as the U.S. ships entered the Strait of Hormuz for their 8 1/2-hour passage through the 50-mile-long channel.

The convoy had just entered the strait when a Saudi AWACS radar surveillance plane detected a number of F4s taking off from the air base.

"They got within radar range of the {USS} Kidd and they came over land," said Capt. William Mathis of the USS Fox, the point ship in the convoy. "The Kidd detected them, issued warnings to them, and they turned around and went back north," said Mathis.

Another Navy official said the Iranian F4s were warned to turn around by American F14s from the aircraft carrier USS Constellation, which launched patrol fighters to cover the convoy's passage through the strait.

"If they would have continued to come in," said Fox's tactical information officer Mike Scharf, "we would let them know if they continue in they could be standing in danger -- they get ample warning to turn away or let us know what their intentions are."

The convoy also sailed along the edge of Iran's wartime "exclusion zone." During the night, the Fox had to execute a sharp right turn to avoid colliding with a small fishing boat.

Also yesterday, the convoy passed a Soviet tanker, believed to be one of three chartered to Kuwait. A Soviet frigate, the Ladnyy, was spotted as well, observing the convoy from a distance of about 15 miles.

"He's just standing off, just fooling around," Lt. Michael Malarkey, a watch officer aboard the Fox, told reporters.

Fox's captain, Mathis, said Navy officials were negotiating with Kuwait to allow U.S. warships to tie up at Kuwaiti naval facilities during the period the tankers are taking on crude oil and natural gas. Earlier, western sources said Kuwait has promised to provide free fuel to the U.S. fleet on escort patrol.

McCartney also reported the following from Bonn:

Velayati's one-day visit to Bonn reflected a new effort by West Germany, and particularly Foreign Minister Hans-Dietrich Genscher, to seek better relations with Iran. Velayati was the first high-ranking official from Iran to visit West Germany since the 1979 Islamic revolution.

Velayati said the new U.S. military presence in the gulf was contributing to increased tension in the region. But he said that Iran was sticking to its position of striking ships only in response to Iraqi attacks.

"Undoubtedly the presence of the U.S. fleet in the Persian Gulf is a factor contributing to the escalation of tension," Velayati said.

"Our conditions and the nature of our confrontation are crystal clear . . . . If the Iraqis stop attacking ships, then no ship will be attacked in the Persian Gulf at all," Velayati said.