SADDAM HUSSEIN TAKRITI, Iraq's cunning and tryannical ruler, sent his army into Iran last week in search of a limited military victory that would establish him as the dominant force in the Arab world and in the global petroleum politics of the 1980s.

Although Iraq's assualt on Iran's frontiers and oil industry erupted with stunning suddenness for much of the world, the campaign had been months in the making and represents a carefully calculated gamble by Iraq's leadership.

The immediate aim of the campaign was to lessen the direct threat posed to Baghdad's Ba'athist government by Iran's revolutionary mullahs and their leader, Ayatollah Ruhollah Khomeini. The Iraqis have sought to humiliate the mullahs and possibly to provoke an uprising against them.

Behind that goal, however, lay the naked ambition of Saddam, as the 42-year-old ex-gunman and lawyer is popularly known. He is determined to wrench the pendulum of Arab political power away from Cairo toward Baghdad by offering a modern version of Gamal Abdel Nasser's pan-Arab crusade.

His troops, who claimed by the weekend to have taken a little more than 100 square miles of Iraqi-claimed territory away from the Iranian army, have not brought him a sufficiently clear victory to guarantee that such grandiose results are on the horizon.

But with its initial ground successes, Iraq has hastened the dismemberment of the collapsing Persian empire, an accomplishment that will stir Arab national pride at the apparent beating the Aryans of Iran are being handed, bringing a new power equation to the region.

It will:

Affect American and Soviet rivalry in Middle East and Persian Gulf regions that Iraq sits astride. Soviet opportunities -- at least in the short run -- will probably be enhanced.

Seriously complicate the American hostage dilemma in Tehran, where a Khomeini-headed government may now be too weak to release the 52 American captives and survive.

Exert strong pressure on Saudi Arabia, which Saddam carefully wooed before going to war, to swing further out of its strongly pro-American orbit and join Iraq in opposing superpower influence in the Gulf.

Reshape the politics of OPEC. Whether by occupying the oil-producing Khuzistan region, or by destroying Iran's oil industry. Iraq seems intent on eliminating Iran as a force within OPEC. Iraqi occupation of a major part of the oil fields in Arab-populated Khuzistan would make Iraq as important an oil power as Saudi Arabia.

Provide an aggressive redefinition of the non-aligned movement, which Saddam had been chosen to head formally in 1982. Saddam clearly wants to replace the anti-colonial political strategy that Nasser used in the 1950s with a new brand of resource-based nationalism strong enough to break the economic imperialism that he feels has succeeded colonialism.

These are audacious challenges for anyone to pose, but particularly for a man who has spent most of the past decade combatting internal plots to remove him from office and executing all visible rivals. Saddam has to know that failure in the battle against Iran could leave his body swinging from a lamppost in Baghdad.

Eleven Iraqis were hung in the streets of Baghdad in 1970, allegedly for being Israeli agents. The highly credible stories of torture and sudden executions that have filtered out of Iraq since have earned its rulers an image of wild and savage unpredictability, an image that could be reinforced by casual reading of the headlines about the new war.

But much of the image is carefully calculated for the intimidating effect it has at home and abroad. Saddam's political motivation and his extended build-up to the attack on Iran underscores the careful calculations that have gone into it.

Saddam is banking on the force of economic nationalism in the Third World, an army that has shown an ability to learn from its battlefield experiences, and the relative weakness of the two superpowers in the Gulf region at the moment to make his gamble succeed.

He was able last week to launch his troops into a geopolitical vacuum. He found the dream foe for an Arab army by attacking a government the United States cannot possibly support, politically or militarily.

The Iran-Iraq conflict caused the world to hold its breath last week because of the threat posed to oil shipping from the Gulf, but it found the Carter administration with neither carrots or sticks to brandish to bring a halt to the fighting. The best President Carter could manage was to endorse the big-power vacuum that Saddam helped create and which he exploited with skill last week.

"We want declarations, not actions," one U.S. diplomat told a European official last week as they discussed the danger of almost any of the options available to the West, such as the idea of a multinational fleet to protect the shipping lanes of the Strait of Hormuz.

The continuing dilemma of the hostages in Iran places severe limitations, of course, on what the Carter administration can do.

That may have been a central fact in Saddam's decision to respond now to months of provocation by Khomeini, who has repeatedly called for the overthrow of Arab governments not motivated by his brand of fundamentalism. Indications by the ayatollah and President Carter this month that a possible solution to the hostage deadlock was in sight must have caused the Iraqis to wonder how much longer America's hands would be tied in dealing with its former ally and arms client.

But the empty U.S. chair in the high-stakes game being played out along the Shatt-al-Arab is also due to the failure of the Carter administration to chart realistic policies for Iraq and Saudi Arabia. These two nations have drawn closer together in the wake of Khomeini's Islamic revolution and in the continuing fallout of the Camp David peace accords that have isolated Egypt in the Arab world.

With Saddam, the White House has abandoned serious policy planning for what one analyst calls a series of "fanciful flirtations" that have gone nowhere. The administration has consistently been overly confident about its ability to manipulate the inherent organizations between Islam and communism and the course of events in Iraq, Iran and Saudi Arabia.

But last week Saddam showed more talent at manipulation than did the superpowers or his Arab brothers and neighbors, many of whom, in the past, have called him "the butcher of Baghdad" or worse.

Now they are praising Saddam or remaining silent in the face of Baghdad's casting of the conflict as an Arab-Persian one. Baghdad Radio filled the air with denunciations of the "Persian magicians led by Khomeini," openly appealing to the racial sterotype many Arabs have of the Persians as a dangerous, devious people. Saddam succeeded quickly in wrapping himself in the Arab world's dislike of "al ajem" -- the non-Arab Moslems of the east.

Saddam's life has been one daring gamble after another, many against enormous odds. He failed in 1959 when he attempted to gun down Iraq's president in the street and was wounded himself. But he and the closely knit clan from the village of Takrit that surrounds Saddam perservered and achieved complete power in 1968.

Saddam won his first big challenge when he nationalized British oil interests in his country and then rode out the kind of international boycott that helped bring down Iran's Mohammed Mossadegh two decades earlier. But Saddam correctly perceived that the energy crisis was reshaping the rules of the political game in the Middle East and figured out how to fit those changes to his goals.

In 1974, the shah of Iran, backed by the United States and Israel, set out to bring Saddam down by supporting the Kurdish rebellion in northeastern Iraq. The Iraqi army suffered embarrassing reverses early in the campaing and Saddam's position appeared to be in peril.

But his army gradually learned to use the massive quantities of sophisticated arms the Russians poured in. And the troops the shah sent in to help the Kurds performed poorly in a foreshadowing of the command and morale problems that caused the Iranian army to disintegrate during Khomeini's taking of power in 1979.

When the shah decided to abandon the Kurds and take the best deal he could get in March, 1975 -- taking control of the parcels of territory along the estuary that Iraq is now winning back -- the United States acquiesced and help set in motion the events that led to this week's bloodletting along the Shattal-Arab.

American analysts have been impressed with the way Iraqi forces applied the lessons of the 1975 campaign in moving into Khuzistan last week. They single out Iraq's effective coordination of air stakes and the fast cutting of major supply routes by Iraqi infantry.

This has been achieved, Arab diplomats friendly to the United States point out, by Russian weapons in the hands of an Arab army.

The attack has brought reality to Saddam's attempt to project Iraq as the Arab world's dominant military power now that Egypt has taken itself out of the war with Israel by signing the Camp David accords. And the outcome of the battle will clearly establish whether Iraq has become the "new Iran" -- the military power in the Gulf.

Even though it would mean a strengthening of one of the most bitter opponents of the Camp David peace agreement, a modest victory by Iraq that would lead to Khomeini's downfall is probably an appealing prospect for different reasons for American policy makers and an American public sickened by the ayatollah's acceptance of hostage-taking.

The most likely alternative scenario at this point is an extremely dangerous one that casts a long shadow over the oil operations of Kuwait, Saudi Arabia and the United Arab Emirates.

The conflict could cool down without a formal ceasefire in the next few days as Islamic countries step up mediation efforts and as Iranian militarly supplies dwindle. But it is difficult to imagine Khomeini being able to accept the terms Iraq demands for a ceasefire.

Iran's military could try to regroup and repeat its surprising military ability to mount deadly bombing raids on Baghdad and on Iraq's own oil installations. This would lead to a mutual war of attrition without unpredictable offensives that would make a shambles of shipments in the northern end off the Gulf. This would in turn accelerate the fragmentation of Iran and its institutions, encouraging the restive Kurds and other minority groups to throw off Persian control, perhaps with Iraqi help.

And as they did last week, both Tehran and Baghdad would then concentrate their appeals on the war's course to Moscow. Iran would again ask that the Soviet arms flow to Baghdad be cut off while Iraq would want to keep it open. The Soviet Union, as a consequence, would be well positioned to try to broker and end of the fighting between the two countries and enhance its role in a region where American prestige has been steadily slipping over the past two years.

Saddam has kept the Soviet Union on a tight leash inside Iraq, using the friendship and cooperation treaty he signed with it in 1972 to ensure continuing weapons delivery from Moscow while ignoring Russian attempts to spread its influence in the Gulf. Saddam has severely restricted the Soviet diplomatic and cultural presence in Iraq while actively working to lessen their influence in the Yemens.

In his increasingly frequent talks with the Saudi royal family, Saddam appears to be pushing the Saudis to use the superpower of their choice for arms and trade reasons, but to restrict American influence inside Saudi Arabia and in the Gulf.

Senior policymakers in the Carter administration have frequently discounted the likelihood of the Saudis making any serious moves toward such a model. The president's national security adviser, Zbigniew Brzezinski, in particularly seems to feel that the Saudis and ultimately even Saddam have no place to go but the United States, despite the heavy baggage that American policy on Israel creates for Arab rulers.

Ultimately, that thesis, as well as Saddam's neck, is on the line in the fighting that has been raging along the Shatt-al-Arab.