Iraqi warplanes broke a three-week lull in the Persian Gulf tanker war today with an attack that set a supertanker ablaze and killed six of its crew members, including two British officers.

Six other seamen were critically burned in the attack on the 115,000-ton World Knight about 40 miles southwest of Iran's Kharg Island oil shipping terminal in an Iraqi-declared war zone. Iranian Navy helicopters lifted them and other surviving members of the crew from the blazing tanker. At least one salvage company tugboat responding to the distress call reportedly stayed on the scene to fight the fire, according to The Associated Press.

A military communique issued in Baghdad said Iraqi jets had attacked two "naval targets" in the gulf, but there was no independent confirmation of a second ship being hit today.

The communique, which repeated previous warnings to ships using Kharg Island, said the attack was designed "to prevent the Iranian regime from using its oil revenues in financing its aggressive aims against Iraq."

The British Foreign Office said it would make a formal protest "once the facts are clear" about the death of the two British officers in the attack, according to Reuter.

"We deplore this attack as we do all attacks on neutral shipping in the gulf," the Foreign Office said. "This again emphasizes the urgent need to see an early settlement to this tragic conflict."

Lloyd's, the London insurance exchange, and gulf sources said the ship was attacked as it headed for Kharg Island to pick up Iranian oil. They said that when the tanker radioed for help, the operator said it had been hit by a "bomb." In the past, rockets and missiles have been used by both Iraq and Iran. Iraqi warplanes most often have used French-made Exocet missiles.

The World Knight was reported to be owned by the Greek company Niarchos and operated by Hong Kong shipping magnate Y.K. Pao's World-Wide Shipping Group. It was registered to Liberia. Marine shipping sources said the crew was made up of five British officers and 33 seamen from Hong Kong, whose nationalities were not immediately known.

The attack brought to an end the latest lull in the gulf tanker war that has seen about 30 ships damaged since late March in sporadic attacks by Iran and Iraq. No tanker has been reported hit since Sept. 16, when Iran attacked the South Korean-owned supertanker Royal Colombo and the Greek-owned supertanker Med Heron in the central sector of the gulf. The latest spate of Iraqi attacks was between Sept. 10 and 13.

No large oil tanker had been seriously damaged in recent months, although six persons were killed when the West German supply ship Seetrans 21 was hit and sunk by Iraqi planes on Sept. 13.

It was not immediately clear why Iraq decided to resume its raids at this time, although Iraq previously has said it regards tankers bound for Kharg Island as fair game as long as Iran does not allow ships to load at Iraqi ports in the gulf.

The Iraqi attacks have been aimed at attracting international attention to the gulf war and at disrupting the export of Iranian oil to inflict damage on Iran's economy and to exert pressure on the Tehran government to agree to participate in efforts to end the war.

Iraq also has sought to increase economic pressure on Iran recently by hitting industrial centers. On Sept. 22, Iraq's warplanes attacked the huge $4 billion Japanese petrochemical plant at Bandar Khomeini at the head of the gulf.

Japanese technicians working at the complex, which has not been completed, were temporarily withdrawn once again after having just returned to the project under heavy Iranian pressure.

Iraqi planes also attacked the Kharg Island terminal on Sept. 20, but no serious damage was reported then.