Just a year ago, the shah of Iran left for a "short holiday" abroad that effectively ended 2,500 years of monarchy in a country that still is in the throes of one of the 20th century's few authentic revolutions.

The outward semblance of law and order, so carefully cultivated by Shah Mohammad Reza Pahlavi at the cost of increasingly repressive methods, collapsed before a kaleidoscope of diffused power that often seemed to border on anarchy.

Now, what one critic calls "the institutionalization of anarchy" characterizes the revolution; its keynote is unpredictability.

The United States, which somehow assumed it had come to a workable understanding with the revolution, paid the price of its political naivete. The captured embassy files, whose unburned documents have served to discredit the United States and moderate Iranians ranging from former prime minister Mehdi Bazargan to Ayatollah Kazem Shariatmadari, the spiritual leader of turbulent Azerbaijan, provide examples.

Yet, if that sort of setting of political scores is a classic feature of revolutions, Iran still wallows in a sea of political innocence. Indeed, that may have been the shah's principal legacy to a people he determinedly kept from meaningful political activity.

Orchestrating both the shah's downfall and the aftermath has been Ayatollah Ruhollah Khomeini, at 79 every bit as autocratic as his fallen archenemy and more like him than his fervent religious admirers care to admit.

Yet despite Khomeini's one-man rule from the distance of his modest establishment of the Shiite Moslem holy city of Qom, life remains more open and relaxed even today than at any time except the final months of the shah's rule, which he then already had been undermined.

Iranians, once a secretive, closed people, now talk about everything under the sun. They feel free to criticize and praise, laugh at or defend a government with which many, in their hearts, are unhappy.

Thus, the leaders are on safe ground in claiming that as revolutions go, theirs has been relatively evenhanded. The rulers have executed fewer than 700 figures from the shah's government and accumulated bad marks less for that than for the arbitrary punishment of prostitutes or adulterers whose sentences may be death in one revolutionary court or 20 lashes in another.

However such things are judged abroad, for most Iranians they are less awful than the shah's record of arbitrary arrests, torture and political repression.

Theft, pilferage and general lawlessness -- often the work of the vigilante-like local revolutionary committees -- have become an unpleasant, if accepted part of postrevolutionary Iran.

Corruption, so prevalent under the shah, has continued in different forms, but the scale is smaller than before. Liquor, although banned under Islam, is available at a price. Narcotics, especially morphine base, opium and herion, are enjoying a booming trade with shipments moving west through Turkey. Smuggling is enjoying a renaissance.

Iran's armed forces, once self-proclaimed guardians of the free world's Persian Gulf oil and described as second only to Israel's in the Middle East, are in a shambles.

Naked to the prospect of Soviet aggression and at loggerheads with its former American protectors, revolutionary Iran seems unconcerned, despite the knowledge that the American, French and Russian revolutions all eventually had to face invading armies.

Thus things fall apart. The middle-class exodus continues, removing what Khomeini scathingly has called the "rotten brains" contaminated with Western culture. Bilingual secretaries are hard to find. The Finance Ministry is said to lack competent accountants.

In theory, the revolution's permanent institutions should be in place in little more than a month. The first round of the presidental race is scheduled for Jan. 25 and parliamentary elections are due in late February or early March.

Yet even though Khomeini has decided that the clergy should not run for presidental office, that does not mean that mullahs will not be the power behind the throne.

Increasingly, such formal offices are seen as irrelevant. It is not just that Khomeini is the final arbiter on almost everything, a privilege enshrined in his hand-tailored constitution.

Nor is it just that Khomeini has managed to cut down to size any group or individual trying to act indenpendently.

Rather it is the logic of revolution.

Like the shah, the imam, as Iranians call Khomeini, has proved more adept at foreign affairs than in dealing with the thicket of domestic politics.

Militant Islam, incarnated by Khomeini, sent shock waves out across the once-slumbering Moselm masses -- from the Philippines to North Africa -- with a simple, iconoclastic message to the people to unseat their rulers.

Nowhere was the message more clearly heard, and more deeply feared, than in the conservative Arab states of the oil-rich Arabian Peninsula.

At home, religious radicals shoved aside gradualists both in and outside the clergy. They seized the U.S. Embassy Nov. 4, provoking a confrontation with the superpower held responsible for the shah's material and moral excesses. It was an exercise designed to cleanse Iran of Western influence by humiliating the West.

Amid Iran's political anarchy, the shah's hopes of turning Iran into the world's fifth industrial power by the end of the century have crumbled, in part because Khomeini's radical economists advocated agricultural self-sufficiency and mistrusted uran industrialization.

Only Iran's oil revenues -- which remained at the same level despite halved exports, as world prices doubled -- kept the economy afloat.

Instead of carrying out its promised "small is beautiful" purge of the swollen bureaucracy, the revolution through its nationalizations actually increased the number of government employes from 800,000 to an estimated 1.2 million.

Throughout the shah's reign sporadic violence, in some cases bordering on civil war. accompanied demands for autonomy from minorities making up roughly half Iran's population. By contrast, Khomeini has shown some inclination to accept the minorities' demands for some representation within a federal system.

Still, the prospect is for more turbulence, especially in Kurdistan, for with a listless Army, the central government is unable to enforce its will.

Indeed the government apparently prefers risking foreign invasion to rebuilding a strong military that could challenge its authority. The leadership now relies on the Revolutionary Guards, a loyalist militia that is incapable of putting down any organized insurrection.

Suspicion of strong institutions such as the military has been at the heart of Shiite Islam's strength. The mullahs who helped overthrow the shah succeeded through a loose network of mosques, and thus were impervious to any central authority, including the shah's.

As for the shah, Iranians -- who for the most part went wild with joy when he flew off into exile -- today hardly bothered to remember the anniversary date.

The surfeit of politics over the past two years has produced a public diffidence that allows the extreme right and the extreme left to fight for power in a seeming vacuum.

The Revolutionary Council, which was supposed to be the ultimate power center, has proved impotent in the face of power without the responsibility exercised by Khomeini and the radical Islamic students holding the hostages at the U.S. Embassy.

The right is now ascendant, destroying the reputations of liberal politicians with the same kind of oversimplified labels the shah so loved.

The left, from the pro-Moscow Tudeh party which echoes Khomeini's every word, to the former urban guerrillas in the Marxist Fedayeen and ultrareligious Mujahideen, are infinitely better organized.

Furthermore, the guerrillas are well-armed.