BAGHDAD - A day before provincial elections that could shift the local power balance, Iraq imposed a nationwide lockdown yesterday - the most sweeping security measure since the deadliest years of the insurgency.

The move underscored Iraqi leaders' desperation to make sure the vote seals a sense of stability after six years of conflict.

Although election-related and other violence has been limited, authorities ordered cars off city streets, sealed borders and closed airports.

The precautions show that the consequences run deeper than just the outcome of today's balloting for 440 seats on provincial councils.

Voting carried off without major attacks or charges of irregularities would give a big boost to Iraqi authorities as the U.S. military hands over more responsibilities.

Serious bloodshed or voting chaos could steal momentum from supporters of a fast-paced withdrawal of U.S. combat troops next year.

Traffic bans were ordered for Baghdad and other major cities. The closely monitored frontiers with Iran and Syria were among borders that were sealed. A nighttime curfew also was in place, to thwart extremist groups that plant roadside bombs under cover of darkness.

Double-ring cordons were planned for the thousands of polling sites - in schools, offices and civic centers - stretching from the foothills in the far north to the Persian Gulf in the south.

Women civilians were recruited to search potential female suicide bombers.

The U.S. military assisted Iraqi forces in the security preparations, but commanders said they would intervene only if needed.

Results are not expected for days. But it could take weeks of dealmaking to determine which parties have gained control of key areas such as Baghdad, the Shiite south, and the former Sunni insurgent strongholds of Anbar province in the west.

There are more than 14,000 candidates. It is the first time large numbers of them have felt secure enough to openly campaign since the U.S.-led invasion that toppled Saddam Hussein in 2003.

'Fruits of democracy'

But the flood of candidates also brings potential confusion. There are more than 2,600 alone in the Baghdad area for 57 seats, turning the ballot paper into a dizzying exercise in picking both a party and a candidate.

"We are tasting the fruits of democracy," Prime Minister Nouri al-Maliki said.

It hasn't been without pain. Gunmen killed three candidates Thursday.

The provincial councils have no direct sway in national affairs but carry significant authority through their ability to allocate funds.

In this election, they also may offer a road map for coming political tussles and trends. The Shiite-led government may have the most hanging in the balance.

Maliki's Dawa bloc has been facing off against Iraq's largest Shiite party, the Supreme Islamic Iraqi Council, which has close ties to Iran but has also forged a rapport with Washington.

A strong showing by the Supreme Council would feed its desire to claim control of the national government in elections later this year and establish a self-governing region in the oil-rich Shiite south.

'Rule of the turban'

There also appears to be a backlash to the Shiite religious parties - or as many Iraqis say, "the rule of the turban" - from some secular Iraqis and particularly Sunnis.

The religious parties, which control southern Iraq, are seen as corrupt and unable to deliver needed services.

Iraq's minority Sunnis mostly stayed away from the last provincial elections, in 2005 - protesting the U.S.-led occupation but also fearing being attacked on polling lines by Sunni extremists.

The boycott handed Shiites and Kurds a disproportionate share of power. In the province that includes Mosul, where Sunnis are 60 percent of the population, the minority Kurds won 31 of 41 council seats.

Not only are Sunnis likely to pick up substantial numbers of council seats this time, Iraq's Sunni hierarchy itself could be reordered.

In Anbar province, the Sunni tribes that rose up against al-Qaeda and other insurgents in a turning point of the war are now seeking council seats to increase their role in national affairs.

Their gains could come at the expense of the Sunni Iraqi Islamic party in the current government.

The voting covers 14 of Iraq's 18 provinces and there are 15 million eligible voters.

Elections are scheduled for later in the northern Kurdish autonomous region and have been postponed in the province around oil-rich Kirkuk, where ethnic groups could not agree on a power-sharing formula.