The three-week-old war between Iran and Iraq appears to have strengthened Iranian President Abol Hassan Bani-Sadr against his domestic political rivals, but there are signs that the continuing power struggle is hampering the effectiveness of the Iranian Army.

Among specialists in the U.S. administration, meanwhile, there is growing suspicion that Iraq's prosecution of the war, which so far has been baffling, may be aimed at depopulating Iran's oil-producing Khuzestan Province and splitting it off from the rest of the country.

Although Iraq, by default, has become the sentimental favorite in this war for many Americans, a clear-cut Iraqi victory involving a direct or indirect takeover of Khuzestan may not be in U.S. interests.

So far, however, there is no sign of any decisive victory, and neither side's armed forces have been particularly impressive in battle. In fact, military specialists say, Iraq's poor performance has made the Iranians look good. But a current Iraqi offensive and the continuing disarray of the Iranian military leave the outcome in doubt.

According to Pentagon and State Department specialists on Iran, Bani-Sadr's Moslem clerical rivals are anxious to forestall the rise of a military strongman who eventually could threaten their authority. This continuing distrust of the regular Army, which formed the late shah's main power base before the Iranian revolution, has contributed to Iran's inability so far to mount an effective counterattack against the Iraqi invaders, the analysts believe.

The Iranian president, on the other hand, has advocated greater reliance on the regular Army and has personally ordered the release of some jailed officers to help carry on the war.

Apparently recognizing the problem and siding with Bani-Sadr, Iranian revolutionary leader Ayatollah Ruhollah Khomeini yesterday decreed that all matters related to the war were the responsibility of a Supreme Defense Council. Tehran's official radio said the council would coordinate all military activities and that "no groups or individuals shall disobey its orders."

This appeared to be an effort to put militiamen of the various revolutionary Guards -- forces run largely by the Moslem clerics of the Islamic Republican Party -- under a centralized command. The seven-member council is headed by Bani-Sadr and includes military leaders and Khomeini aides.According to the radio, one parliamentary deputy will also serve on the council.

"Bani-Sadr is still fighting a tremendous internal battle over the Army," a Defense Department analyst said. "There is still a group that fears the Army more than the Iraqis, and that will probably be a critical factor in the outcome of this thing."

While Bani-Sadr's Moslem clerical rivals are the most prominent opponents of resurrecting a strong regular Army, their fears are shared by Iranian leftists. After the shah's overthrow in February 1979, leftist guerrilla groups tried to promote a "people's revolutionary army" by forming soldiers' committees within the armed forces.

The continuing suspicion of the regular Army was shown recently when Iranian authorities took Tehran-based reporters on a tour of defensive positions in the Khuzestan provincial capital of Ahwaz. According to the reporters, mullahs and Revolutionary Guards kept trying to divert attention from the role of military officers and keep themselves in the spotlight.

"They don't want to create any heroes," a Pentagon analyst here said. "In Tehran, they're almost oblivious to the war; they're just worried about who's going to emerge."

So far, that leadership role has fallen largely on Bani-sadr, who has enhanced his hitherto tattered presidential image by making the major decisions on the conduct of the war, touring battle zones, visiting the wounded and generally demonstrating courage and calm.

Bani-Sadr also has benefited from the relatively creditable performance up to now of the Iranian armed forces.

By the same token, however, Bani-Sadr could be the big loser if the tide of the battle turns even more decisively against Iran, analysts here say. He could also be hurt domestically, they add, if the regular armed forces fail to repel the Iraqi invaders while the Revolutionary Guards -- who are associated more with his rivals -- continue to put up a diehard, even if losing, defense.

One factor that may be on Iran's side is its abundance of munitions. Because of the late shah Mohammad Reza Pahlavi's obesssion with stockpiling military material, Iran may be in better shape than the Iraqis as far as supplies are concerned, some specialists here believe.

The Iranians'main problem is that they do not know, in many cases, where to find or how to maintain and operate available equipment.

For example, Iran still has an estimated 2,400 Maverick air-to-ground missiles acquired under the shah. The Maverick, a small television-guided tactical missile that is highly effective against small targets such as armored vehicles, gun positions or even ships, has not yet been used by the Iranian Air Force. The Iranians also are believed to have vast caches of ammunition, including thousands of artillery rounds, stashed away in depots in the mountains north of Tehran.

In addition, Iran has arms factories that had been turning out considerable quantities of small arms, ammunition and artillery shells before the revolution. It is not known whether these plants are still operating, but Pentagon analysts believe that if they are not they probably could be reactivated.