BAGHDAD -- Ahmed Chalabi, the onetime U.S. ally, is in the limelight again, and his actions are proving no less controversial than they did years ago.

On the eve of Iraq's parliamentary elections, Chalabi is driving an effort aimed at weeding out candidates tied to Saddam Hussein's Baath Party. Chalabi is reprising a role he played after the U.S.-led invasion -- which many critics believe he helped facilitate with faulty intelligence -- and, in the process, is infuriating American officials and some Iraqis, who suspect his motive is to bolster his own political bloc.

Chalabi, a Shiite, has defended the work of the commission he is leading as legal and crucial during a period of transition to Iraq's first sovereign government. But his reemergence on the political scene has rankled U.S. officials and fueled concerns that Sunnis and other secular Iraqis will be marginalized.

Some Iraqi and U.S. officials think Chalabi might have his eyes on the ultimate prize, however unlikely he can attain it.

"Even if it kills him, he's going to stay in Iraq to try to become prime minister," said Ezzat Shahbandar, a Shiite lawmaker from a competing slate who has known Chalabi for more than 20 years. "This issue is the only tool he has, because he has nothing else going for him."

Chalabi fell out of favor with the Americans in 2004, after they accused him of spying for Iran. The year before, though, he had been appointed to head a U.S.-formed commission to rid the government of officials tied to Hussein's regime.

The hasty, wholesale purge that the commission conducted is now widely seen as a catalyst of the insurgency and Iraq's sectarian war. Today, however, Chalabi remains at the helm of a similar "de-Baathification" panel, the Justice and Accountability Commission, because parliament has not appointed new members.

When the commission recently announced the disqualification of nearly 500 candidates from the March 7 parliamentary elections, critics noted that candidates from Sunni-led and mixed secular coalitions were disproportionately targeted. Many of those ousted were rivals of Chalabi's bloc.

A court impaneled to review the cases carried out a cursory review behind closed doors. Candidates were allowed to submit written appeals but were never told the specific nature of the allegations against them. The court disqualified 145 candidates; most others dropped out or their parties replaced them.

Now the disqualifications are widening sectarian and religious divides in Iraq, even as it continues to reel from decades of authoritarian rule, occupation and bloodshed. This week, in an apparent attempt to allay some of the bitterness, the government said it would reinstate 20,000 former army officers ousted because of their ties to Hussein.

But the political disqualifications threaten to undermine the elections, overshadowing campaign issues such as security, unemployment and basic services.

At the center of it all is Chalabi.