Iraq's top Shi'ite clerics and politicians are seeking to unite the country's majority behind Iraq's draft constitution. But they are facing resistance from two powerful Shi'ite clerics in Baghdad and Basra. With the country's Sunni Arabs already opposed to the document, it is not yet clear whether there will be enough Shi'ite unity for the constitution to pass next month in a national referendum.

The most crucial endorsement of Iraq's draft constitution came late Thursday from Grand Ayatollah Ali al-Sistani, arguably the most revered and most powerful Shi'ite cleric in the country.

Aides to the reclusive cleric say they have been given orders to promote 'yes' votes for Iraq's October 15 referendum. Mr. Sistani is also expected to issue a religious edict, called a fatwa, in favor of the draft.

In January, the ayatollah's fatwa for all Shi'ites to participate in Iraq's elections prompted millions to defy insurgent threats and vote. The ballot gave the Muslim sect an overwhelming majority in the National Assembly and government.

Mr. Sistani's endorsement of the constitution has given huge momentum to another Shi'ite religious cleric, Abdel Aziz al-Hakim.

Members of his Supreme Council for Islamic Revolution in Iraq party, which has close ties to Iran and dominates Iraq's current interim government, played a major role in drafting the charter.

Speaking at a meeting Saturday in Baghdad, Mr. Hakim called voting 'yes' in the referendum a religious duty for all Shi'ites. He described those who oppose the constitution as enemies of Iraq.

Mr. Hakim says enemies of Iraq are trying to prevent the country from developing into a free nation, and want to deny the Iraqi people the rights and guarantees they deserve.

A number of prominent clerics, tribal leaders, and politicians from Iraq's Sunni Arab minority have already vowed to mobilize their communities to reject the draft constitution in next month's referendum. Sunnis fear the document, which endorses federalism in place of a strong central government, would give Shi'ites in the south and Kurds in the north too much power, and lead to the breakup of the country.

But in a threat to the unity of the Shi'ite vote, the leaders of two factions, with large support bases in Baghdad and in Iraq's second-largest city of Basra, have also voiced their objections to the charter. Both factional leaders are rivals of Abdel Aziz al-Hakim.

Radical cleric Moqtada al-Sadr, who draws his support mainly among the two-and-a-half million impoverished residents of Baghdad's Sadr City neighborhood, has repeatedly denounced Mr. Hakim's vision of a federalist south.

Mr. Sadr fears that the creation of a Shi'ite semi-autonomous zone there will vastly increase Shi'ite Iran's influence in the south and give Mr. Hakim's political party dominance in the area.

Moqtada al-Sadr has encouraged voter registration, but remains uncommitted on the constitution.

On Saturday, meanwhile, the conservative leader of one of Basra's largest Shi'ite political parties, Ayatollah Mohammed Yaqoubi, openly defied Grand Ayatollah Sistani's endorsement of the constitution by instructing his followers to vote 'no' on October 15th.

Sources in Basra say Mr. Yaqoubi and his followers are unhappy that the constitution fails to make Sharia, or Islamic law, the sole legal system in Iraq. The current draft proposes that Sharia be only one source of legislation.

Shi'ite unity is crucial to the passage of the constitution. If two-thirds of the voters in any three of Iraq's 18 provinces vote against it, the draft will fail and a new interim government will have to be elected to write another constitution from scratch.