ABOARD THE MARNE, JAN. 20 -- The commander of France's naval forces in the Persian Gulf said today that French warships will fire on Iranian gunboats that refuse to break off attacks on neutral merchant ships when French vessels come to the rescue.

Rear Adm. Guy Labouerie, speaking to reporters aboard this flagship for France's 22-ship Indian Ocean fleet, said he was spelling out French rules of engagement in the area following an incident last weekend between the French corvette Dupleix and Iranian gunboats in the Strait of Hormuz.

He called on all nations with warships in the region to adopt a similar posture toward Iran, which he described as a "de facto" intervention in Iranian attacks in the name of "humanitarian" assistance to the crews of undefended merchant vessels calling for help.

Labouerie said French commanders would not seek to provoke Iran, but added that it was necessary to state clearly how French warships would respond to distress calls and that there were "some consequences of the Iran-Iraq war that we won't accept on the sea."

"We cannot see other ships burning with their crew without helping," he said.

Although he insisted that he was not articulating a new policy, the admiral's statements go further toward a commitment to intervene in Iranian gunboat attacks against neutral shipping than those of any other western nation whose warships are deployed in the area.

Gulf Arab governments and shipping officials have been seeking greater protection for oil tankers and cargo vessels flying so-called flags of convenience or other foreign flags and who pass unescorted through the 550-mile waterway. In 1987, Iran mounted a record number of attacks against commercial shipping in response to Iraqi air strikes on ships exporting Iran's oil.

French intervention, as described by Labouerie, also goes beyond U.S. naval policy in the gulf, which prohibits U.S. commanders from firing on attacking Iranian gunboats unless U.S.-flag vessels are threatened. U.S. naval commanders have sought expanded authority to intervene and stop Iranian attacks on non-U.S. flag vessels, but Reagan administration officials are reported to oppose such a move.

During a trip to the gulf two weeks ago, Defense Secretary Frank Carlucci also appeared to oppose any expansion of the U.S. role, indicating that he intended to keep the U.S. military mission in the strategic waterway limited in scope. "We are not policing every area of the high seas for every country," he said then.

Washington Post correspondent Edward Cody reported from Paris, however, that in discussions with French officials on his way home from the gulf, Carlucci, according to a diplomatic source with access to the talks, raised what was described as his "personal idea" of expanding the U.S. role in the gulf to include protection of neutral shipping.

The prospect was discussed with Arab leaders during Carlucci's trip to the gulf, the source said, in response to complaints by Saudis and others that the limited U.S. role left most shipping unprotected.

The source said Carlucci's idea envisioned increased military and financial cooperation from the Arab states of the gulf and Western Europeans, including France, which has the second-largest western naval fleet in the gulf.

Carlucci, the source said, hoped that presenting the proposal as a coordinated force, with Arabs sharing some of the cost, would help gain U.S. congressional acceptance. France, according to the source, said it would consider the Carlucci proposal if the Arab gulf states were prepared to be a part of such a force.

{Pentagon spokesman Fred Hoffman said in Washington that Carlucci had discussed "various options" in his talks with French officials, but he added, "That shouldn't be taken that changes are contemplated."

{Carlucci reported on Tuesday to President Reagan and other senior White House officials on his visit to the gulf but Hoffman said that the meeting did not constitute a formal review of the U.S. gulf policy.}

U.S. warships have provided humanitarian and rescue assistance to neutral shipping after Iranian attacks, but one U.S. frigate captain said this week, "We're not going to get in the middle of anything."

The incident that became the watershed for Labouerie's declaration of French naval policy occurred Saturday as the Dupleix was escorting the French mine sweeper Orion through the Strait of Hormuz.

Dupleix's commander, Claude Musset, told reporters in an interview on the bridge of the Dupleix that he heard at 3:42 p.m the radioed distress call of a Liberian-registered chemical tanker, Rainbow, about 11 miles behind him, and turned his ship around to respond.

The French warship steamed at full speed back through the strait and when it reached the reported location of the Rainbow off the Omani coast, its lookouts spotted smoke billowing from the Rainbow's crew quarters.

"At 3:50 p.m., we saw three speedboats, which fired three rockets at Rainbow without reaching her," said Musset.

As the Dupleix closed the distance to the burning ship and came within range of the rocket fire directed at the Rainbow by the Iranian attackers, the warship "called on the gunboats to stop their threatening shots or she would fire," Musset said, adding, "The speedboats stopped shooting and moved away."

"The fact that Dupleix went quickly close to the tanker obviously stopped the attack and saved Rainbow and crew," Musset said.

Elaborating on Musset's remarks, Labouerie said through an interpreter, "I think everybody should do the same thing . . . . The international war fleets are here to reduce tensions."

Citing another incident on the night of Dec. 22, Musset said a French warship responded to the distress call of the Liberian-flag tanker Stena Concordia. The warship "headed straight for the position of the tanker and this had the effect of stopping the attack by an Iranian frigate," Musset added.