BAGHDAD — The leader of Iraq’s biggest Shiite militia movement has quietly resumed seminary studies toward attaining the title of ayatollah — a goal that could make firebrand cleric Moqtada al-Sadr and his Mahdi Army an even more formidable power broker in Iraq.

Mr. Sadr’s objectives — described to the Associated Press by close aides — are part of increasingly bitter Shiite-on-Shiite battles for control of Iraq’s southern oil fields, the lucrative pilgrim trade to Shiite holy cities and the nation’s strategic Persian Gulf outlet.

The endgame among Iraq’s majority Shiites also means long-term influence over Iraqi political and financial affairs as the Pentagon and its allies look to scale down their military presence in the coming year.

Mr. Sadr’s backers remain main players in the showdowns across the region, where fears of even more bloodshed are rising following Wednesday’s triple car bombing in one of the area’s main urban hubs. At least 25 people were killed and scores wounded.

But Mr. Sadr — who was last seen publicly in May — is also confronting the most serious challenges to his influence, which includes sway over a bloc in parliament and a militia force that numbers as many as 60,000 by some estimates.

Becoming an ayatollah — one of the highest Shiite clerical positions — would give the 33-year-old Mr. Sadr an important new voice and aura.

It also would give him fresh clout to challenge his top rival, the Supreme Islamic Iraqi Council, which looks to Iranian-born Grand Ayatollah Ali al-Sistani as its highest religious authority and has its own armed wing, the Badr Brigade, which have been largely absorbed into Iraqi security forces.

Mr. Sadr often stresses his Iraqi and Arab roots and rejects suggestions that he is beholden to Persian Iran, the world’s Shiite heavyweight and the benefactor of many Shiite politicians.

As an ayatollah, his views and fatwas, or religious edicts, would resonate with even more authority as the battles heat up for sway over Iraq’s Shiite heartland.

Comparisons are often drawn between Mr. Sadr’s strategy — a mix of militia strength, well-tuned street politics, and social outreach — and the hallmarks of Hezbollah, which has been influenced by Lebanon’s top Shiite cleric, Grand Ayatollah Mohammed Hussein Fadlallah, as well as Ayatollah Ruhollah Khomeini, founder of Iran’s 1979 Islam Revolution.

“If … Moqtada becomes a religious authority, the entire movement will grow stronger,” one of the aides who described Mr. Sadr’s seminary studies to the AP said. The Sadr associates — three in all — spoke on condition of anonymity because they are not authorized to share the information with the press. Their accounts, made in separate interviews, were in broad agreement.

Mr. Sadr currently has the relatively low title of hojat al-Islam, which leaves his supporters no choice but to seek religious guidance from top establishment clerics — many of whom Mr. Sadr sees as out of touch with common Iraqis and accuses of acquiescing to Washington’s demands.

The aides said Mr. Sadr was currently on a path to achieve ayatollah rank possibly by 2010 or earlier. His studies were under the supervision of senior clerics in the Shiite holy city of Najaf — where Mr. Sadr’s Mahdi Army fought grinding urban battles with American forces in 2004.

In 2000, Mr. Sadr enrolled in “outside research” — roughly the equivalent of a doctoral program. Afghan-born Grand Ayatollah Ahmed Issaq al-Fayadh, one of Najaf’s four top clerics, supervised him when he joined, but Mr. Sadr’s attendance has been spotty since 2003. Successful candidates qualify for ayatollah upon completion of the rigorous Islamic studies. But it’s also necessary to have a family pedigree in Islamic scholarship and a following among seminary students and laymen.