The shah of Iran has taken steps to defuse his most serious crisis in the past 15 years by uncharacteristically adopting a softer line against anti-government demonstrators.

In deciding to place some of the blame for day long rioting two weeks ago in the city of Tabriz, on the hamhanded tactics of provincial officials, Shah Modammed Reza Pahlavi apparently has sided - at least for the time being - with his more dovish advisers.

To quell the latest rioting, which bordered on an insurrection, the Iranian army sent its British and American made tanks into the streets of the northwest Iranian provincial capital and ordered troops to open fire on demonstrators.

Official accounts said nine people were killed and 125 wounded, but other sources listed about 100 dead and more than 300 wounded.

In the wake of the Tabriz rioting, hardline government elements reportedly urged a major crackdown on the opposition - consisting of isolated human rights activists and the powerful Shi'ite Moslem leadership - and called for exemplary punishment.

But after initially blaming the Tabriz violence on Communists and Moslem extremists, the shah maneuvered nimbly by firing local officials for "negiligence" leading to the rioting.

Singled out as scapegoats in the Tabriz purge were not just the underlings - such as the provincial police chief and the local head of police intelligence - but Eskandar Azmoudeh, governor general of the sometimes turbulent East Azerbaijan Province bordering the Soviet Union.

The autocratic 58-year-old shah's new tactics not only have reduced tensions caused by the Tabriz events but also are thought by the Tabriz events but also are thought by analysts to stand a good chance of limiting damage to the governments prestige, which he has worked so tirelessly to promote.

"This has been the biggest shocl to the shah since 1963" if when there was an abortive coup -" but unfortunately for us, he has emerged strengthened," a dissident leader said.

The move also has diluted criticism of the shah for trampling on the religious opposition when his police forces fired on a crowd of Moslem demonstrators in the holy city of Qom Jan. 9.

The shah is credited with understanding the traditional Moslem leadership's latent disruptive power in this fundamentally religious country, and its potential ability to channel discontent arising from an exodus from rural areas scarce and expensive urban housing, inflation and other ills.

Neither the Moslem opposition nor the leaders of the nascent - and still vulnerable - human rights movement are indulging in any gloating over the shah's handling of the Tabriz rioting.

Whatever his present forebearance, they know the shah now has the pretext - as well as the power - to crush their disorganized ranks if he so chooses.

Still, the fact remains that the shah chose - in this case, at least - to concede the possibility of official fault.

The government-controlled press hammered home the point by noting "many people think some officials actually fueled or even generated the unrest by their irresponsible behavior.

"But for these officials," read a typical commentary in the English-language newspaper Kayhan International, "These demonstrations would have remained peaceful, they feel."

For Iranians long accustomed to reading between the lines of their censored newspapers, that was tantamount to official recognition of the opposition's charge the government provocation played a part in sparking the Tabriz rioting.

The opposition claimed that the violence - in which rioters attacked scores of banks, stores, government buildings and movie houses which stayed open despite a strike called by the Moslem leadership - stemmed from provincial government action to prevent the faithful from worshipping at a large Tabriz mosque.

Literally locking them out of the Masjed-E-Jomeh Mosque was the heavy-handed government way of trying to undercut the Shi'ite Moslem leadership's appeal for peaceful strikes and worship to commemorate those killed at Qom, dissidents said.

According to the government, six civillians were killed at QOM. But religious leaders have insisted more than 70 persons lost their lives when police fired with automatic weapons on a crowd demonstrating outside the holey city's Aazam Mosque.

Relations between the authorities and the religious leaders in QOM had been tense in the wake of a government-inspired newpaper article described as personally insulting to Ayatollah Ruhollah Khomeini, Iran's most influential Shi'ite leader who led 1963 coup attempt and now is in exicle.

Yet without the government's heavy-handedness, many Iranians appear convinced the regime could well have avoided open conflict with the religious leadership which has never been much below the surface in this country's history.

The urban guerrillas who occassionally killed American officers and Iranian establishment figures were never considered to have a significant following.

"But this was the first time in years that the religious leadership realized its own strength," an analyst noted.

Both the religious and secular political opposition charge that the shah has violated the 1906 Constitution through an inexorable accumulation of "executive authority," and that he has run roughshod over the judicial and legislative branches.

The political opposition wants the constitution enforced to bring back free elections and allow formation of political parties.

Most dissidents - religious, political, students, professors, lawyers, judges, educated middle class - would agree with the idea of continuing the monarchy. But they also want an independent prime minister and government, which the prideful shah feels would hinder Iran's economic and social development, besides reducing him to a figurehead monarch.

Most dissidents further want freedom for political prisoners, an end to exile and torture, limited jurisdiction for controversial military tribunals, plus various freedoms - notably of speech, press, political parties, association and religion.

In classic illustration of De Tocqueville's theory that unrest occurs when authoritarian regimes ease up, the shah started taking a more tolerant approach to dissidents in early 1976.

By the time the Carter administration took office, the Shah was moving in the suggested path of judicial reform. The American Embassy already had established contact with dissidents without apparently unleashing the Shah's wrath.

Dissident lawyers acknowledge that physical torture has now been abandoned although they claim that investigators for SAVAK, the secret police, still deprive political prisoners of sleep in an effort to obtain confessions.

There have also been reliable reports of severe beatings and torture by lower-level policemen or government agents, but those recently appear to have not been carried out as systematically as before.

Also important has been the increasing use of civil courts instead of military tribunals for political offenders. That reform not only insures that prisoners are not kept in Savak prisons, but enables lawyers to see defendants early in the legal process.

Previously, lawyers had no knowledge of their clients' cases until the defendants were put on trial.

As for political prisoners, Iranian officials claim 1,700 were released last year and 2,200 remain in jail. While agreeing that a number of prisoners were released last year, human rights activists here insist that as many as 10,000 political prisoners remain in custody.

The regime has also tolerated - but not officially recognized - formation in January of a Committee for the Defense of Human Rights as well as the existence of dissident writers and jurists associations.

But the dissidents' most telling success so far was the news conference they managed to hold - the first in 15 years - during the recent visit here of United Nations Secretary-General Kurt Waldheim.

At the press conference, they presented a lengthy open letter to Waldheim, signed by 30 prominent Iranians, describing 15 areas of alleged human rights' violations.

Yet the regime can still show its teeth. Shortly after the Shah's mid-November visit to the United States, an estimated 220 students were arrested, and hundreds of others beaten, by riot police and men dressed in civilian clothes believed to be Savak agents. Their behavior was apparently dictated by the Shah's anger at hostile student demonstrations here and in Washington.

President Carter's brief New Year's Eve stopover here disappointed some dissidents because of his praise for the shah. But others credit the Carter administration with bringing about some of the key judicial reforms.

"I think the United States does not want to change the situation in depth," a human rights activist said, "just the facade."

Noting what dissidents take to be Carter's toned-down defense of human rights here, he said: "We think it is because Iranian oil and arms purchases are more important to Washington.

Still, many dissidents hope Carter will prevent the shah from carrying out serious retaliation against them.

"The religious leaders are inexperienced in politics," a leading dissident lawyer complained. "We are against this kind of violence which plays into the shahs hands.

"We are just starting out and must convince the people that they can oppose the government freely and calmly," he added.

On that score the shah has yet to show his hand. But he has sworn publicly to push ahead with his own brand of liberalization "despite the violence he claims is caused by "black and red imperialism."

That is his political shorthand for religious and leftwing opposition, and for many Iranians, it is a not entirely happy reminder of the tension of the early 1960s.