By complaining about American pressures, French President Francois Mitterrand mustered Gallic sympathies for his slow-motion arms buildup in Chad.

But the same political method is proving less effective in another, more ominous war that is causing friction between Paris and Washington.

American officials have expressed concern that French delivery of five Super Etendard planes equipped with Exocet missiles to Baghdad next month could dangerously escalate the scale of fighting in the Iranian-Iraqi war that has dragged on for nearly three years.

The Iraqis are reportedly intending to use the highly effective air-launched missiles against Iranian oil installations in the Persian Gulf. If that happens, Iran is likely to retaliate with attacks on Arab oil targets.

A major conflagration in the gulf could effectively shut down an important share of energy supplies from the region, with drastic consequences for the fragile world economic recovery.

The impact of such a scenario on the oil-dependent French economy has not been lost on commentators usually favorable to the Mitterrand government.

The newspaper Le Monde, which has served as the president's policy messenger through interviews during the Chad crisis, has raised serious doubts about the so-called two-year "loan" of Etendards and Exocets to Iraq.

"The Americans, after all, are perhaps not always wrong," a Le Monde editorial noted this weekend. "France today finds itself in the detestable position of donor to one of the protagonists of the gulf war."

After a policy toward the Chad conflict based on prudent military restraint to encourage peace negotiations, the Mitterrand government seems embarrassed by the exposure of its role as a principal weapons supplier to one of the parties in a war with vast repercussions.

The Socialists came to power vowing to end France's role as the gendarme of Africa in pursuit of "blood and treasure," as Mitterrand said in campaign speeches.

The same yardstick, however, has not been applied to French arms sales, which have grown in commercial importance under the Socialists because of the need to curtail a woeful trade deficit that may exceed $7 billion this year.

In the scramble for foreign markets, France has turned in recent years to the Middle East in the hope that big-ticket items, such as arms and plane sales, might boost a depressed economy.

While the major arms sales push began under conservative French governments, Mitterrand has been compelled to nurture such relations, however distasteful he may find the "merchant of death" label, because they remain one of the few bright spots in the French economy.

France accelerated its trade relations with Iraq when then-prime minister Jacques Chirac encouraged major investments in Iraq during the oil boom of the 1970s.

In return for favorable oil deals, France began to supplant the Soviet Union as Iraq's chief weapons source. France also built a nuclear reactor for Iraq that was destroyed in an Israeli bombing raid in 1981.

When Mitterrand took power two years ago, he continued to pursue the arms-for-oil relationship.

When the war eroded Iraq's ability to pay its bills, France was forced to accept a renegotiation of Baghdad's debt to Paris, now estimated at nearly $5 billion.

The same mercantilist considerations were said to have influenced France's more benign perspective toward Libyan Col. Muammar Qaddafi's ambitions in Chad when the policy quarrel with the United States burst into the open.

When Libyan-backed rebels launched their assault two months ago, the French government sought to avoid any antagonism toward Qaddafi and has maintained close contacts with Tripoli throughout the crisis.

French Foreign Ministry officials admitted that since the start of this year, Libya had been designated a key North African country that offered good possibilities for more lucrative trade arrangements.

Libya provides oil to France and in recent years has evolved into a major customer for French military equipment.

As the Chad crisis grew more intense, Mitterrand reaped political benefits at home by rejecting East-West implications seen by an American administration that believes Qaddafi is an Islamic crusader toiling for Moscow's interests.

The French president won support for his opposition to big-power intervention in conflicts among developing countries that he believes are rooted in ancient political rivalries, as in Chad, or intolerable economic exploitation, as in Central America.

He is finding it more difficult, however, to reconcile those views with France's role as arms supplier in the brutal war of attrition between Iran and Iraq--and the French public seems to sense it.