THANKS, but no thanks: So Grand Ayatollah Ali-Mu hammad Sistani answered an invitation to visit Iran.

The invitation was conveyed to Sistani at his home in Najaf, Iraq, on behalf of the Tehran leadership by Ali-Akbar Hashemi Rafsanjani, a mid-ranking mullah and a former Islamic Republic president.

At a press conference after his audience with Sistani, the Iranian visitor didn't say why the grand ayatollah had demurred, only that Sistani had "offered convincing reasons for declining the invitation."

The episode is of political interest for a number of reasons.

To start with, recall that Sistani, who was born in Iran, is an Iranian citizen and holds an Iranian passport. Although he has lived in Iraq since his teens, the 78-year-old theologian always made a point of visiting Iran at least once a year - until 1979, when the mullahs, led by Ruhollah Khomeini, seized power in Tehran.

Thus, his refusal to visit Iran is a rejection of the system created by Khomeini. Indeed, millions of expatriate Iranians refuse to visit their homeland because of their opposition to the Khomeinist regime.

Sistani couldn't visit Iran without meeting Ali Khamenei, a mid-ranking mullah presented by the government as the "supreme guide" of the world Islamic community, and thereby virtually endorsing that extravagant claim, which he rejects. Nor could Khamenei call on Sistani - for he'd then be acknowledging Sistani's status as the primus inter pares of the Shiite clergy.

A visit to Iran by Sistani - recognized as the world's most senior Shiite cleric, with millions of followers throughout Iran - would be a major political event.

Put under house arrest in Najaf in 1989, Sistani had had little organized contact with Iran until 2003, when the US-led Coalition overthrew Saddam Hussein's regime. Sistani was then able to reopen his seminary, revive contacts with outside Shiite communities and dispatch emissaries to set up offices throughout Iran.

He has now appointed representatives to more than 800 Iranian localities, creating the largest network of any grand ayatollah. By unofficial estimates, his network now collects the biggest share of private religious donations in Iran. Its offices finance thousands of theological students and run social-support services for the poor and the needy in both Iran and Iraq.

What explains Sistani's spectacular success? To start with, most Shiites regard him as the spiritual heir of the late Grand Ayatollah Abol-Qassem Mussavi Kho'i, the last major 20th century Shiite theologian.

Then, too, Sistani represents the classical quietist version of Shiism - based on a separation of the mosque and the state. That is, classical Shiism rejects rule by the clergy - a theory developed by Khomeini under the slogan "guardianship of the cleric."

Those Shiites, perhaps a majority, who want a clergy that is independent of government now look to Najaf as the true center of their faith. Many regard the Khomeinist version of Shiism that Tehran espouses as a political doctrine rather than a religious faith.

In that context, the grand ayatollahs of Najaf, with Sistani as their head, are seen as protectors of the faith against those who wish to transform it into an anti-Western, anti-modern and anti-democratic ideology.

Some observers wonder why Sistani agreed to grant Rafsanjani an audience when he'd refused a similar request from Islamic Republic President Mahmoud Ahmadinejad during the latter's visit to Iraq last year. Sources close to Sistani cite "a question of protocol": If he'd called on Ahmadinejad at the Iranian consulate in Najaf, it would have amounted to an acknowledgment of the superior status of political over religious authority. And for Ahmadinejad to call at Sistani's home would have acknowledged that the grand ayatollah's status was above that of the Islamic Republic president, angering Khamenei back in Tehran.

Sistani could receive Rafsanjani because the latter had no qualms about being treated like any other "believer" wishing to see the grand ayatollah.

Rafsanjani becomes the most senior Islamic Republic figure to pay tribute to Sistani, acknowledging his position as the highest-ranking Shiite theologian. This is of special significance because Rafsanjani is also the speaker of the Assembly of Experts - a body of 92 mullahs who could dismiss the "supreme guide" in Tehran.

As the power struggle sharpens in Tehran, the encounter in Najaf is bound to encourage those in Iran who call for the abolition of the "supreme guide" and a return to classical Shiism, in which government and religion are distinct spaces.

Classical Shiism is already functioning in Iraq, where Sistani continues to play a major role. By going to Najaf, Rafsanjani may have posed the question: If it works in Iraq, couldn't it be tried in Iran, too?