BAGHDAD — Iraq imposed a nationwide security lockdown as voting began today in key regional elections with measures not seen since the deadliest years of the insurgency. The security underscored the high stakes for Iraqi leaders desperate to portray stability after nearly six years of conflict.

Although violence is down sharply, authorities were unwilling to take any risks. They ordered cars off city streets, sealed borders and closed airports.

The top-to-bottom precautions show that the consequences run deeper than just the outcome of voting for the 440 seats on influential provincial councils across Iraq.

Voting carried off without major attacks or charges of irregularities would give an important boost to Iraqi authorities as the U.S. military hands over more responsibilities to them. But serious bloodshed or voting chaos could steal momentum from those who support a fast-paced withdrawal of U.S. combat troops next year.

The election is also a possible dress rehearsal for bigger showdowns this year when the U.S.-allied government of Prime Minister Nouri al-Maliki could face challenges for power.

"Our security is very well-prepared," said the deputy interior minister, Iden Khalid.

Traffic bans were ordered for Baghdad and other major cities. A nighttime curfew was in place, apparently to block extremist groups that plant roadside bombs under cover of darkness.

Double-ring cordons are planned for the thousands of polling sites in schools, offices and civic centers. In many places, female teachers and other civilians were recruited to help search for possible female suicide bombers.

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

More than 14,000 candidates have joined the races, marking the first time that large numbers of Iraqi politicians have openly campaigned since the U.S.-led invasion that toppled Saddam Hussein began in 2003.

But the flood of candidates also brings potential confusion. There are more than 2,600 in the Baghdad area for 57 seats.

"We are tasting the fruits of democracy," al-Maliki said at a campaign stop for some political supporters.

Iraq’s minority Sunnis widely stayed away from the last provincial elections in 2005. The boycott handed Shiites and Kurds a disproportionate share of power.

Now Sunnis are likely to pick up substantial numbers of council seats, and Iraq’s Sunni hierarchy could be reordered.