Iran is promoting a conservative cleric close to its supreme leader as a possible successor for the aging spiritual leader of Iraq's Shiites, a move that would give Tehran a powerful platform to influence its neighbor, according to figures close to Iraq's religious leadership.

The 81-year-old spiritual leader, Grand Ayatollah Ali al-Sistani, is one of the most influential figures in Iraq, revered by its Shiite majority as well as by Shiites around the world. In the years after the 2003 U.S.-led invasion and fall of Saddam Hussein, he was strong enough to shape the new Iraq, forcing American leaders and Iraqi politicians to revise parts of their transition plans he objected to.

The man Iran is maneuvering in hopes of eventually replacing him is Grand Ayatollah Mahmoud Hashemi Shahroudi, a prominent insider in the clerical hierarchy that rules Iran. He was the head of Iran's judiciary for 10 years until 2009, playing a major role in suppressing the country's reform movement, and sits on one of Iran's main ruling councils.

Shahroudi has started to build a presence in Najaf, the Iraqi holy city of dozens of seminaries that is the center of Shiism's religious leadership, to which many of the world's 200 million Shiites turn for spiritual and political guidance. Posters bearing his portrait have sprung up in the Baghdad district of Sadr City, a bastion of Shiite activism and home to some 2.5 million Shiites.

Iran's growing influence in Iraq -- through the economy and ties with Shiite politicians in Baghdad -- is already a source of alarm to the United States and its Gulf Arab allies who see Shiite-majority Iran as a rival.

It would boost Tehran's voice in Iraq even more if Shahroudi ever succeeds al-Sistani as "al-marjaa al-akbar," or "the greatest object of emulation."

The 63-year-old Shahroudi would likely take an even more assertive political role than al-Sistani has. Al-Sistani adheres to a "quietist" school of Shiism that rejects formal rule by clerics, in contrast to Iran's school in which clerics hold ultimate power.

Also, al-Sistani has lived in seclusion for years -- he is thought not to have left his Najaf house since 2004 -- and some feel he has grown out of sync with Iraq's new generation of young and empowered Shiites. Disillusioned over unemployment and erratic services, many young Shiites are looking for a more dynamic religious leadership to counter what they see as the rising power of Sunni fundamentalists in the Arab world.

"Iraq's Shiites are deeply politicized and they have had enough of traditional marjaiyah (religious authorities) like al-Sistani's," said one insider in Najaf, who is in daily contact with the city's top clerics. "Iran is taking advantage of this by working energetically to replace him with one of its own."

The insider is one of six who are well connected to the Shiites' secretive religious establishment in Najaf and in Baghdad. They said Shahroudi appears to be angling for the post. They spoke to The Associated Press on condition of anonymity because of the sensitivity of the subject.

Al-Sistani, who was treated in London for heart problems in 2004, remains healthy and alert, according to visitors who saw him recently. But his advanced age has fueled speculation about his succession in Najaf.

But the succession does not necessarily have to wait until al-Sistani's death. It could effectively take place if al-Sistani is deemed too old to guide his followers.

The position of al-marjaa al-akbar is considered the highest in Shia Islam's spiritual hierarchy, more elevated than the several dozen clerics with "marjaa" -- or "object of emulation" -- status in the Shiite world. Pious Shiites generally choose a marjaa to follow. Al-Sistani has been al-marjaa al-akbar since the 1990s.

Filling the post is done by an informal process of consensus among senior and middle-ranking clerics, aimed at choosing the learned and respected figure. "Campaigning" for it means showing religious clout among Shiites in general and in Najaf specifically.

Ibrahim al-Baghdadi, Shahroudi's top aide in Najaf, would not say if Shahroudi has ambitions for the position. Morteza Monajjem, a spokesman for Shahroudi's office in the holy city of Qom, Iran's religious capital, said the cleric "has no plan to stand next to other marjaas" and "has not officially defined himself as a marjaa."

Still, Shahroudi is laying the necessary groundwork.

He opened a representative office in Najaf in October and plans to visit the city soon, according to al-Baghdadi.

He has begun paying monthly stipends to poor seminary students, organizing "study circles" and collecting the "khoms" from followers -- a tithe of a fifth of one's income. He has sent cleric-deputies to Shiite provinces in Iraq, al-Baghdadi said. He has also increased his issuing of fatwas, or religious edicts, in response to questions sent to his website.

Any ayatollah with aspirations of becoming a marjaa must write a religious textbook known as a "Tawdih al-Masail," or "Clarification of Issues," laying out rules for daily religious practice. Shahroudi published his just over a year ago.

Shahroudi is already known to be the spiritual leader of powerful Iraqi factions, including followers of the Badr Organization as well as most members of the Iranian-backed Shiite Hezbollah Brigades militia active in southern Iraq, and Asaib Ahl al-Haq, a hardline faction.

Among his students in Qom were Hassan Nasrallah, leader of Lebanon's Hezbollah movement, and Humam Hamoudi, a prominent Iraqi politician.

Shahroudi is also believed to have replaced a grand ayatollah who died in 2010 as the spiritual mentor of the Dawa Party, Iraq's oldest and most powerful Shiite political group. Iraqi Prime Minister Nouri al-Maliki, the Dawa leader, visited Shahroudi during a recent visit to Iran.

Shahroudi was born in Najaf to Iranian parents in a family of clerics that claims descent from the Prophet Muhammad. He studied under Grand Ayatollah Mohammed Baqir al-Sadr, a prominent scholar credited with modernizing Shiite doctrine before he was executed by Saddam in 1980.

Shahroudi fled a 1979 crackdown against Shiites and took refuge in Iran.

There, he became the first leader of the Supreme Council of the Islamic Revolution in Iraq, a major opposition group of Iraqi Shiite exiles. The group became a major political player in post-Saddam Iraq and its successor party is in al-Maliki's ruling coalition.

Shahroudi also rose in Iran's clerical leadership. He is so close to supreme leader Ayatollah Ali Khamenei that he has been cited by many observers as his possible successor.

Still, the Najaf insiders caution there are challenges in his path to succeed al-Sistani.

Muqtada al-Sadr, the young anti-American cleric whose followers have 40 of parliament's 325 seats, has been in Iran studying to become a marjaa. But he is believed to need several more years before he can reach the rank of ayatollah, a status below marjaa, according to one of his aides in Iraq.

One of Shahroudi's former students in Qom -- now an Iraqi politician -- said Shahroudi is strongly positioned.

"He is relatively young, he is familiar with modern day issues and has impeccable family pedigree," he said. "The Shiite street wants a dynamic marjaa who can compensate it for the failure of the government."