BAGHDAD, Iraq - Iraq's deeply divided Shiites, Sunnis and Kurds took their struggle over the nation's future to the ballot box Saturday, voting in a fierce competition over a new constitution aimed at establishing a democracy after decades of dictatorship.

Whole families marched to the polls, standing in line by the hundreds in the crucial electoral battleground provinces of central Iraq that have mixed populations and will be decisive in whether the draft constitution will pass or fail.

In towns where Sunni Arabs largely boycotted the voting in January parliamentary elections, they were now eager to cast ballots, most of them hoping to defeat a draft charter they fear will set in stone their domination by Iraq's Shiite majority.

"The government can't just sew together an outfit and dress the people up by force. We do not see ourselves or see our future in this draft," said Gazwan Abdul Sattar, 27-year-old Sunni teacher in Mosul after voting "no" in the northern city of Mosul.

In a nearby mostly Kurdish neighborhood of the city, Bahar Saleh gave her support to the constitution. "This constitution will at last give the Kurds their lost rights," the 34-year-old housewife said, coming from the polls with the red-and-green Kurdish flag wrapped around her body.

In the south, the heartland of Iraq's Shiites, women in head-to-toe veils and men emerged from the polling stations flashing victory signs with fingers stained with indelible, violet ink to ensure everyone votes only once. Shiites appeared to be responding in mass to the call by their top cleric, Grand Ayatollah Ali al-Sistani, to support the charter, and some Shiite cities reported a higher turnout than the January vote.

Insurgents attacked five of Baghdad's 1,200 polling stations with shootings and bombs, wounding seven voters, but there were no major attacks reported as U.S. and Iraqi forces clamped down with major security measures around balloting sites.

American troops in Humvees rattled down Baghdad streets in patrols, while Iraqi soldiers and police ringed polling stations at schools and other public buildings protected by concrete barriers and barbed wire. Iraqi soldiers armed with heavy machine guns looked over polling sites from nearby rooftops.

U.S. troops in tanks and armored vehicles stood not far away as helicopters hovered overhead. Driving was banned to stop suicide car bombings by Sunni-led insurgents determined to wreck the vote.

"Today, I came to vote because I am tired of terrorists, and I want the country to be safe again," said Zeinab Sahib, a 30-year-old mother of three, one of the first voters at a school in the mainly Shiite neighborhood of Karrada in Baghdad. "This constitution means unity and hope."

The polls opened at 7 a.m., just hours after government workers restored power that insurgents had sabotaged in the northern part of the country Friday night, plunging the Iraqi capital and surrounding towns into darkness.

In the central Baghdad area of Khulani, where Sunnis and Shiites both live, a steady stream of voters entered a large polling station after being searched three times. Old men and women who could barely walk with canes were searched, as were young mothers wearing chadors and carrying infants.

Within three hours of the poll's start, at least a quarter of registered voters cast ballots in Baghdad's biggest Sunni Arab district, Azamiyah, where in January hardly a soul was seen in the January vote.

"This is all wrong. I said 'no' to a constitution written by the Americans," said Jilan Shaker, 22, a laborer who showed up at an Azamiyah polling station in shorts and plastic sandals.

In Baghdad, President Jalal Talabani and Prime Minister Ibrahim al-Jaafari were shown live on Al-Iraqiya television voting in a hall in the heavily fortified Green Zone, where parliament and the U.S. Embassy are based.

"The constitution will pave the way for a national unity," said al-Jaafari. "It is a historical day, and I am optimistic that the Iraqis will say 'yes.'

The United States hopes that the constitution's success will pave the way for withdrawing American troops.

At Iraq's approximately 6,100 polling stations, voters marked their paper ballot "yes" or "no" under one question, written in Arabic and Kurdish: "Do you agree on the permanent constitution project?"

The country's Shiite majority - some 60 percent of its 27 million people - and the Kurds - another 20 percent - support the approximately 140-article charter, which provides them with autonomy in the regions where they are concentrated in the north and south.

The Sunni Arab minority, which dominated the country under Saddam and forms the backbone of the insurgency, widely opposes the draft, convinced its federalist system will eventually tear the country apart into Shiite and Kurdish mini-states in the south and north, leaving Sunnis in an impoverished center. Many of them feel the document doesn't sufficiently support Iraq's Arab character.

Last-minute amendments in the constitution, adopted Wednesday, promise Sunnis the chance to try to change the charter more deeply later, prompting one Sunni Arab group - the Iraqi Islamic Party - to support the draft Saturday. Most others still reject it.

Shiites and Kurds can easily gain a simple majority in favor of the constitution in Saturday's vote. But that is not enough to ensure passage. If two-thirds of voters in any three of Iraq's 18 provinces vote "no," the charter will be defeated.

There are four provinces where Sunni Arab opponents are hoping to make that threshold: Anbar, Ninevah, Salahuddin and Diyala, all with Sunni majorities. But all of those except Anbar also have significant Shiite and Kurdish populations mixed in.

So competition was at its fiercest in those areas. In the Salahuddin town of Tikrit, which is overwhelmingly Sunni Arab, some 17,000 voters turned out by noon.

But turnout also appeared high in mainly Shiite towns and districts elsewhere in the province. "I believe this constitution will secure women on a lot of issues and will give them a good representation in the National Assembly," said Muna Ali.

In much of the vastly Sunni Arab Anbar province - the main battlefield between insurgents and Iraqi and U.S. troops - residents remained huddled in their homes, and few went to cast votes, fearing militant reprisals or too bitter over a constitution they oppose to participate.

Ramadi, Anbar's capital, looked like a ghost town, with empty streets. At the hour polls opened, insurgents clashed with U.S. troops in the downtown streets.

Only about 70 people had voted in the Anbar town of Haditha, northwest of Baghdad, by midday. Said Ahmad Fliha walked up the hill to the fortified polling station with the help of a relative and Iraqi soldier.

"I'm 75 years old. Everything is finished for me. But I'm going to vote because I want a good future for my children," Fliha said.