The war between Iraq and Iran, which erupted 11 weeks ago with all the earmarks of a short, lopsided conflict, has settled into a protracted war of attrition in which one side is unwilling to mount a new offensive and the other is incapable of it.

As a result, the outcome most likely will be determined not on the battlefield in the classic military sense, but by how long the two countries can sustain their supply lines to the front and on how willing they are to continue fighting in the face of inevitable economic hardships at home.

Those are among the conclusions that emerged from interviews here with Iraqi officials, military analysts and Western and Third World diplomatic observers as Iraq and Iran remain gripped in a struggle that is as perplexing in its inclusiveness as any conflict in recent history.

Every war produces important new lessons for military theorists and tacticians. Analysts of this one have already begun drawing conclusions that they say will be important for the world to bear in mind as it considers the prospects of continuing instability in the Middle East.

Chief among these is that wars between two developing countries need not conform to the usual Third World pattern of short, limited clashes in which each side restricts its objectives to incapacitating the other's armed forces.

The Persian Gulf war has been taken to the economic arena -- the oil installations of Khorramshahr and Abadan on the Iranian side and Basra and Kirkuk on the Iraqi side -- with the declared intention by each side of bringing the other to its knees economically.

"If this is going to be the pattern in the Middle East, then it is an ominous prospect for those of us so dependent on imported oil. Combatants in the Middle East have always scrupulously avoided hitting each other's economic installations. There obviously are new ground rules on this score," said one Western diplomat.

The other major lesson military analysts are digesting is the pitfall faced by a stable, apparently militarily superior nation when it takes on an unstable revolutionary regime.

"This war shows the danger of getting into a fight with a country in the midst of a revolutionary process. It is like trying to have a boxing match with a madman. You can't stop if you want to, because in a revolutionary state reactions are not normal," said a military analyst from an Asian country.

Iraqi President Saddam Hussein has made unmistakable overtures to Iran for a cease-fire, observers noted, but the Iranian regime shows little sign of giving them serious attention. It is as if the Iranians, still locked in revolutionary zeal, veiw the war as a logical extension of the popular uprising they launched against the monarchy of the late shah two years ago.

On the ground, both sides appear positioned for a long struggle of attrition, as if intending to wear the other down gradually until an undeclared but de facto cease-fire results from sheer exhaustion.

Iraq is believed to have all or part of nine of its 12 army divisions committed to the front, either in direct confrontation with the enemy or in backup positions.

But Iraq appears to be following a deliberately restrained strategy, advancing cautiously and infrequently and then, when confronted with resistance, halting to establish secure positions. The infantry has been used sparingly, but heavy artillery shelling -- a favorite of Soviet tacticians -- has preceded every advance until tanks and armored personnel carriers are able to creep forward.

"Today the Iraqis' objective is to get Iran to agree to a cease-fire, and then bargain for territorial concessions," said one foreign military analyst here. "They are already well within Iran. What purpose would be served by taking another town or rushing another 50 kilometers forward?"

In the air war, Iraq, in the view of these observers, has also shown restraint since inflicting extensive damage on Iran's oil facilities in the first weeks of the conflict. It has relied almost exclusively on low-level raids by its Mig fighter-bombers, forgoing high-altitude bombing runs by its Soviet-made TU22 and IL28 bombers.

Military analysts here discount reports that the Iraqis have had trouble maintaining and repairing their sophisticated aircraft, and they attribute the restraint to a political decision motivated by a reluctance to suffer heavy losses.

"They could launch 500 sorties a day if they wanted, but what is the point in it? Remember, the more you use, the more you lose," a military analyst said.

The key question for the Iraqis is whether they can maintain a supply of materiel for the war effort in the face of diminishing sources of resupply. It is widely assumed here that Saddam Hussein, despite his confidence that Iraq would defeat Iran quickly, had stockpiled military supplies against the possibility of a drawn-out war.

Iraqi officials would not say -- and diplomatic military specialists said they do not know for certain -- whether Iraq is still receiving arms from the Soviet Union, although there have been reports that the flow has ended because of a cooling of relations. But analysts said it is likely that Iraq is being resupplied to some extent by Eastern European nations and from other arms markets. Iraq has hostile relations with the other Soviet-equipped Arab states, Syria and Libya.

Several military analysts here said they believe that Iraq can wage war at the current level for at least six months with existing stockpiles and then, with its estimated foreign reserves of $32 billion, continue at a reduced level.

"Time is on Iraq's side," said a diplomatic observer. "It is Iran who is going to feel the effects of a war of attrition first."

Analysts said Iran, sustained by little more than the fanaticism of Ayatollah Ruhollah Khomeini's style of Islam and an enormous pool of manpower, can continue to wage a relatively successful defensive war. After nearly three months of fighting, Iraq still has been unable to take complete control of the port of Khorramshahr, where Revolutionary Guards continue to battle Iraqi troops. But it is just as clear, observers said, that Iran is incapable of mounting a new offensive against the Iraqi Army, and it is doubtful whether the state of its fragmented Army will permit it to do so in the foreseeable future.

"The best they can do is dig in and try to wear the Iraqis down, a diplomatic analyst said. "The Iraqi Army seems to be doing the same thing, which gives you a combination of circumstances that doesn't indicate much change in the situation."