DUBAI, UNITED ARAB EMIRATES, NOV. 6 -- An Iranian speedboat attacked a U.S.-operated Panamanian tanker near here early this morning, indicating that despite U.S. retaliatory measures, Iran's willingness to attack U.S.-linked shipping in the Persian Gulf remains unchanged.

The attack with rocket-propelled grenades on the 103,584-ton Grand Wisdom off the United Arab Emirates port of Jebel Ali, 20 miles west of here, was Iran's first against a foreign tanker in the gulf since one of its Silkworm missiles slammed into the U.S.-flagged Kuwaiti tanker Sea Isle City on Oct. 16.

That attack, which left the Sea Isle City's American captain blinded and 16 other crewmen injured, prompted Washington to shell Iran's Rostam offshore oil drilling platform, which U.S. intelligence officials believe was used for radar surveillance of ships en route to Kuwait.

Today, ship crewmen passing in the vicinity said the Rostam rig was still burning, 17 days after four U.S. destroyers fired 1,000 shells at it.

There were no casualties in today's attack on the Grand Wisdom, according to ship crewmen interviewed by radio telephone. The crewmen said their ship had been hit five times by rocket-propelled grenades, causing a fire in the ship's engine room that took two hours to extinguish.

The crippled tanker was shadowed by the guided missile cruiser USS Rentz as it made its way to anchor off Dubai today, although there was no indication that the Rentz had been protecting the Grand Wisdom when it was attacked.

The U.S. Naval Task Force in the gulf was not expected to consider the attack as grounds for further retaliatory strikes against Iran. The Navy's rules of engagement limit the task force to defending U.S.-flagged vessels in the gulf, not U.S.-managed vessels flying foreign flags.

"An Iranian gunboat hit us with rocket-propelled grenades this morning shortly after dawn," said a ship's radio operator when reached after the fully loaded oil tanker anchored off Dubai. "There was a fire onboard in the engine room but we put it out." Ship salvage officials said they understood the damage was not serious and could be easily repaired.

The attack came hours before "waves of warplanes" attacked Iran's vital petrochemical complex at the port of Bandar Khomeini, according to an Iraqi war communique

The communique said that all planes had returned to base unscathed after "leaving their targets ablaze, and the pilots saw columns of black smoke billowing from their targets."

Iraq also claimed to have hit another "large naval target" -- or oil tanker -- off Iran's coast last night. It was the fifth ship Iraq has claimed to have hit this week, although only one, the Iranian supertanker Taftan, has been confirmed.

Tehran Radio said today that Iran had shot down an Iraqi plane during air attacks yesterday around Iran's main offshore oil loading terminal at Kharg Island. The broadcast said the warplane, believed to be a Soviet-made MiG23, plunged into the sea in flames in Saudi Arabian territorial waters. Baghdad denied the report.

Earlier in the week Iraq acknowledged that Iran had downed one of its planes during a raid on oil installations in Khuzestan Province in southwestern Iran. Tehran claimed it also had captured the pilot.

U.N. Secretary General Javier Perez de Cuellar received replies Monday from Baghdad and Tehran indicating that despite a U.N. Security Council call in July for an immediate cease-fire, the two sides are as far apart as ever.

Iraq has expressed eagerness to comply with a cease-fire, but Iran has insisted that Iraq first be condemned as the aggressor in the seven-year-old gulf war and that it agree to compensate Iran for war damages.

Speeches by such Iranian leaders as the speaker of the Iranian parliament, Hojatoleslam Ali Akbar Hashemi Rafsanjani, and Prime Minister Mir Hossein Mousavi this week have made it clear that Iran sees no possibility of a solution to the war except on the battlefield.

Iranian President Ali Khamenei, addressing the weekly Friday prayer session at Tehran University, renewed his country's attack on the presence of U.S. warships in the gulf to protect reflagged Kuwaiti tankers. Iran has singled out Kuwait for attack in the war because of its support of its neighbor, Iraq.

As crowds chanted, "War, war till victory," and, "The gulf will be President Reagan's burial place," Khamenei declared U.S. policy "declining, baseless and groundless."

The confused state of U.S. policy in the gulf, he said, was to be seen in the crash of the American stock market, the declining value of the dollar and the resignation this week of what he called the U.S. "secretary of war," Caspar W. Weinberger.