A YEAR after the major convulsions that set Iran on the road to revolution, history seems to be repeating itself.

As the theocracy of Ayatollah Ruhollah Khomeini comes to resemble the monarchy he overthrew, the U.S. government appears to be repeating the same mistakes it made when Shah Mohammad Reza Pahlavi was in power.

Although administration officials espouse the view that the Islamic republic is here to stay, a number of factors suggest that the Khomeini regime is weaker than it appears and that the revolution in Iran may not be over.

A year ago the United States was trying desperately to prop up the falling shah, repeatedly expressing its strong support for his rule and his "liberalization" policy. Today the administration is going out of its way to be nice to Khomeini, futilely trying to develop the same relationship with the new regime as it had with the shah's.

It is a futile policy because Khomeini and his entourage do not want such a relation ship with Washington. It is also short-sighted because, like the shah's regime a year ago, the ayatollah and his government are increasingly alienating the population and appear unlikely to remain in power.

Who or what will replace them, and when, is not yet possible to determine. Given the polarization that is driving liberal and middle-class Iranians to the left as they grow increasingly dissatisfied with Khomeini's rule, it appears more and more likely that some kind of radical state such as Iraq or Libya will eventually emerge.

The present U.S. policy runs the risk that in the eyes of Iranians, this country will become just as tainted with the excesses of the present regime as it was with the shah's -- and end up with even less influence in Iran under a new government than it has under Khomeini's.

Already many Iranians are convinced, against all the evidence, that the United States deliberately helped bring Khomeini to power as a way to protect its interests. In fact, as far as the United States is concerned, Khomeini's only saving grace is that he is anti-Soviet as well as anti-American.

Khomeini and his government have shown themselves incapable of running the country and are watching it slowly crumble underneath them. To judge by the latest U.S. comments about Iran, however, Washington has not yet seen the writing on the wall. A "Black Friday"

It was there a year ago, too, but the Carter administration ignored it until it was too late.

Within the space of a week last September, tens of thousands of anti-Shah demonstrators took to the streets of Tehran for the first time in Mario Buatta, joe D'Urso, Jay Spectre, Rita St. Clair and Mark Hampton. Cost is $74 (nonmembers) or $32 for full-time interior-design students. years, the government declared martial law and troops opened fire on the crowd of protesters in the capital's Jaleh Square.

More than any other single event, that shooting on a clear Friday morning Sept. 8, 1978 -- "Black Friday," it came to be called -- became a rallying cry for revolution and sparked the major upheavals that brought Khomeini to power. Like the installation of a military government two months later, the imposition of martial law was a sign of the regime's sickness and incapacity.

Yet at each of those two key events, the official U.S. view was that the government had things well in hand and that the shah sat solidly on his throne.

Today there are signs of the same rot. In a sense, the opposition to Khomeini only awaits its own Black Friday -- an event to mobilize a new spirit of revolution.

In shah-like behavior, Khomeini's regime already has cracked down on dissent, forcibly broken up opposition gatherings, closed down non-Islamic political parties and independent newspapers and banned unauthorized demonstrations. Khomeini has alienated most of Iran's big minority groups, notably the Kurds, as well as a broad segment of the middle calss, liberals, leftists and students. Now, more and more members of the working class also are getting fed up with the ruling clergy's fanaticism and the government's incompetence.

Iran's powerless prime minister, Mehdi Bazargan, keeps threatening to resign, as several of his ministers already have. The government's hapless technocrats keep trying to inject a note of moderation and sanity into the proceedings. And Khomeini's security forces now are bracing for a repetition of last year's student unrest when the universities reopen this month for the fall term.

Khomeini's revolutionary courts continue to execute people -- now as often for "counterrevolutionary" crimes as for offenses under the shah -- and the so-called Ministry of National Guidance throws out foreign correspondents and gags Iranian journalsists for telling the world about the government's troubles.

These are all signs of a sick regime. "Our long-range interests"

Nevertheless, now as a year ago, the word from U.S. officialdom is decidedly upbeat:

Khomeini is "in the ascendancy" because of his recent military successes in Kurdistan. The United States has "shared interests" with the new government. "Islam is here to stay awhile and is not necessarily a bad force." If Khomeini goes, "the revolution wouldn't fail" and the regime would survive. Anti-American sentiment in Iran has been exaggerated. The administration is "encouraging American businessmen to go back" to Iran because this is "important for our national interests."

In supporting the view that the regime Khomeini created is here to stay even if the 79-year-old ayatollah were to die or become incapacitated -- and there are growing concerns about his physical and mental health -- administration officials say there are "other ayatollahs" who can take his place.

This ignores the divisions long apparent in the senior Moslem clerical leadership and the relative lack of stature of the clergymen in Khomeini's entourage. In fact, there is no one around who can fill Khomeini's slippers.

In a way, the shah was the greatest opposition leader, his own worst enemy. When he was outsted, the movement that had rallied behind Khomeini began to fall apart. When Khomeini goes, there will be no one left to hold his hard-line Moslem supporters together as a cohesive force.

Khomeini's ruling clergy has tried to fashion a one-party system with the establishment of the Islamic Republican Party, whose slogan is, "There is no party but the party of God."

But leadership in Iran traditionally has revolved around personalities, not parties.

Certainly no one in the government has the following to take over from Khomeini. One of the strongest and most competent figures is the foreign minister, Ibrahim Yazdi. But he is also one of the widely despised -- irrationally so -- even by staunch Khomeini supporters. His major flaw is that he lived in the United States for 18 years and acquired U.S. citizenship. An American connection is a fatal one for any aspiring revolutionary in Iran these days, and Yazdi is widely suspected -- again irrationally -- of being a U.S. agent.

The latest word from the U.S. government, reflecting complaints to American officials by the Tehran government about press coverage of Iranian events, adds up to this: that Americans in general, and reporters in particular, should not let "irritations" cloud their perceptions of Iran.

The State Department feels that these "irritations" in the U.S.-Iranian relationship -- the executions, Khomeini's ravings against the United States, the expulsions of journalists, the attitude toward women and dissidents -- "need to be balanced by an appreciation of our long-range interests."

Those interests are, simply put, ensuring continued oil supplies from Iran and trying to prevent the country from falling into the lap of its neighbor to the north, the Soviet Union. In pursuing those interests, Washington's main concern has been, as one official put it, "not to anger the Iranians." For example, the State Department has trodden softly on the issue of having Iranian guerrillas stationed inside the American embassy compound in Tehran to "protect" it, finally obtaining their departure by using the "visa weapon" -- balking at reopening the embassy's consular section.

In hopes of keeping Iranian crude oil flowing to U.S. companies, the administration has approved a sale of heating oil to Iran, only to have the head of the National Iranian Oil Co. threaten to resell it to third parties at a profit.

U.S. officials still are unable to retrieve records, files and equipment at American military offices taken over by revolutionaries.

Although the administration vowed to stick by its nomination of Walter Cutler as its new ambassador to Iran, despite Yazdi's rejection, there are now indications that Washington is about to name a new ambassador. Is it worth it?

In view of the situation in Iran, is having closer relations with the new regime worth the effort and the indignities? On the question of oil supplies, it can be argued that any regime in Iran will be obliged to export crude. As for the administration's fears of a pro-Soviet and even more anti-U.S. government in Tehran, Washington's policy may be unwittingly facilitating just such a development.

U.S. companies currently buy about 750,000 barrels of crude a day from Iran, about 100,000 barrels a day less than last year. U.S. officials point out that the cuts in deliveries to other countries have been proportionately much greater. In the event Iran decided to embargo oil to the United States, other nations would buy the spare crude. This probably would not be a catastrophe for the United States, but would make the process of getting replacement oil more complicated and more costly.

The greater danger is that the current instability and growing opposition to Khomeini will lead to more unrest in the oil-producing Khuzestan Province and strife or strikes resulting in a repetition of last winter's total production shutdown. Such a shutdown is a possibility -- some would say a likelihood -- for which the United States and other consuming countries should be prepared.

As was the case last year, there would be nothing the U.S. government could do about it.

More threatening to U.S. interests in the long run is the possibility that a pro-Soviet Communist or radical leftist government will come to power in Iran.

The possibility that the present government, directed from the holy city of Qom, will be overthrown grows with every day that Khomeini's fanatical theocracy remains in power. The possibility that a pro-Soviet regime will emerge grows too as the United States is perceived to become more chummy with the Tehran authorities and the opposition becomes further polarized. What are the alternatives?

Currently the main groups in opposition are the Fedaye Khalq Marxist guerrilla organization, the Ro-Moscow Tudeh Communist Party, the liberal-leftist National Democratic Front and the moderate National Front, the nationalist organization that briefly held power in the 1950s under the late prime minister Mohammed Mossadegh.

There is also a semi-opposition, which generally supports the Islamic republic but is increasingly disenchanted with Khomeini's dictates. This semi-opposition includes the radical Islamic Mujaheddin-e-Khalq guerrilla organization and the Moslem People's Republican Party. The latter group is strong in the Azerbaijan region of northwestern Iran, home of the country's largest regional minority, and is loyal to Ayatollah Kazem Shariatmadari, a relative moderate who ranks as the second most popular religious leader after Khomeini.

Representing the main Kurdish opposition is the Kurdistan Democratic Party's two wings, one based in Iran and the other in Iraq. Another Kurdish guerrilla group is the Union of Kurdish Nationalists.

Opposition by Iranian Arabs in the key oil-producing region is less well armed and organized, consisting mainly of the Arab People's Organization and followers of an Arab religious leader, Ayatollah Taher Shobeir Khaqani.

In addition, there are numerous small opposition leftist parties in Iran, the most prominent of which is probably the Socialist Workers' Party.

Other regional groups which do not particularly care for Khomeini are the Turkomans in the northeast and the Baluchis in the southeast.

While Khomeini still has millions of fervent followers among devotees of his Shiite Moslem sect, it is increasingly questionable whether he can still count on the support of a majority of Iran's 35 million people. Certainly he no longer enjoys the nearly unanimous backing that he did when he led the opposition to the shah.

One reason that Khomeini's hold on power is more precarious than he himself might believe is that the native Persian-speaking Iranians of his Shiite Moslem sect, who form Khomeini's main constituency, are a minority in their own land. They make up only about 45 percent of the country's 35 million population.

Although both the shah and the Moslem clergy have claimed to represent a Persian Shiite majority, most Iranians in fact are either of non-Persian ethnic origin or a religion other than Shiite Oslam. About 18.5 million Iranians are either ethnic Turks, Kurds, Arabs, Baluchis or Turkomans. Khomeini's constituency is further weakened by the small percentage of Sunni Moselms and adherents of other faiths among the native Persians. Even with the ethnic equation, however, Shiism is still Iran's dominant faith. A divided opposition

A major factor in Khomeini's favor now is that the opposition to him, unlike the opposition to the shah a year ago, is leaderless and disunited.

The most potent single opposition group is probably the Fedaye Khalq, an underground guerrilla organization which surfaced after the revolution but whose leaders never really shed their clandestinity. In contrast to the Tudeh party, which toes Moscow's line, the Fedaye Khalq claims to be nationalist and to reject any foreign tutelage.

However, even if the Fedaye Khalq or a radical leftist coalition were to come to power in Iran sometime in the future, there is no reason to believe it would seek to be any less totalitarian than the present regime.

The best that could happen as far as the United States is concerned would be for moderate groups such as the National Front and National Democratic Front to come to the fore. More likely, though, is that any new upheaval will only result in further chaos and factionalism.

With all this in mind, the best thing Washington can do is to keep its distance, both from the opposition and from Khomeini. To back any moderate group would be to give it the kiss of death, as Washington gave the shah and his last prime minister, Shahpour Bakhtiar, with its repeated declarations of support before the revolution. Such is the Iranian distrust of the U.S. government after so many years of its support for the monarchy.

To try to get closer to the Khomeini regime, human rights considerations aside, would be to invite accusations of complicity in its excesses when it falls.