BAGHDAD, Iraq – An Al Qaeda lieutenant in custody in Iraq has confessed to masterminding most of the car bombings in Baghdad, including the bloody 2003 assault on the United Nations headquarters in the capital, authorities said yesterday.

Sami Mohammed Ali Said al-Jaaf, also known as Abu Omar al-Kurdi, “confessed to building approximately 75% of the car bombs used in attacks in Baghdad” since the Iraq war began, according to the interim Iraqi prime minister’s spokesman, Thaer al-Naqib.

Mr. al-Jaaf was taken into custody January 15 and confessed to 32 car bombings, a government statement said, including the bombing of the U.N. headquarters that killed the top U.N. envoy in Iraq, Sergio Vieira de Mello, and 21 other people.

The suspect, a top lieutenant of Al Qaeda’s Iraq leader, Abu Musab al-Zarqawi, also built the car bomb used to attack a shrine in the Shiite holy city of Najaf that killed more than 85 people, including Ayatollah Mohammed Baqir al-Hakim, in August 2003, the statement said.

It said he also assembled the car bomb used in May to assassinate then president of the Iraqi Governing Council, Izzadine Saleem.

Two other terrorists linked to Mr. al- Zarqawi’s terror group also have been arrested. They included the chief of Mr. al-Zarqawi’s propaganda operations and one of the group’s weapons suppliers, the government statement said.

The government offered no evidence to support its claims, and the announcement followed a series of car bombings, kidnappings, and assassinations of Iraqi security personnel, all of which have lowered public morale as the nation prepares for elections next weekend.

Since June 28, when the interim Iraqi government took power, there have been 202 car bombings across Iraq, including 70 in the Baghdad area. The attacks have killed 1,061 people and injured 2,753.

Prime Minister Allawi has been promising to crush the insurgency and restore public order if he holds onto his job in the new government.

In the latest attack, a suicide bomber blew up a carload of explosives yesterday outside the headquarters of Mr. Allawi’s party, wounding at least 10 people in the latest blast claimed by Al Qaeda in Iraq. The violence raised fresh fears about the safety of voters in Sunday’s national elections, which Sunni Muslim insurgents have threatened to sabotage.

Mr. al-Zarqawi has been trying to incite Sunni Arabs against the Shiite majority, playing on Sunni fears that the elections will spell the end of their privileged position in Iraq.

Yesterday’s car bombing struck at a police checkpoint near the offices of Mr. Allawi’s party, the Iraqi National Accord. Police said the guards opened fire moments before the blast, a thunderous explosion that reverberated throughout the city center.

Eight policemen and two civilians were wounded, according to a doctor at Yarmouk Hospital, Mudhar Abdul-Hussein. It was the second suicide attack on the office this month.

In an Internet posting, Al Qaeda in Iraq said the attack was carried out by “one of the young lions in the suicide regiment” against the “agent of the Jews and the Christians.”

An audiotape posted on the Internet a day earlier, purportedly from Mr. al-Zarqawi, declared a “fierce war” on democracy and said anyone who takes part in the elections would be considered “an infidel.”

The authenticity of the tape could not be verified. Mr. al-Zarqawi’s group has been behind many car bombings, beheadings, assassinations, and other attacks in Iraq. America has offered a $25 million reward for his capture or death – the same amount as for Al Qaeda leader Osama bin Laden.

Many Sunnis are expected to boycott Sunday’s elections, either to express opposition to the process or for fear of reprisals. Shiites and Kurds are expected to vote in huge numbers.

Iraqis are to choose a 275-member National Assembly and legislatures in each of the 18 provinces. Voters in the Kurdish-ruled area of the north will also elect a new regional Parliament.

Faced with discontent in the Sunni community, politicians running on a ticket endorsed by Shiite clerics, the United Iraqi Alliance, sought yesterday to dispel fears that they would impose a hard-line Shiite state. A Sunni Muslim on the ticket, Hanin Mohammed Qaddou, said religious rule was “not part of the program and it will not be in the near future.”

Shiite leaders also promised not to seek revenge for attacks by Sunni extremists.

Iraqi officials have announced stringent security measures to protect voters, including closing the borders, extending the hours of curfew, and banning private vehicles. In addition, the 170,000 multinational troops, most of them American, have stepped up security operations, rounding up hundreds of suspected insurgents.

Fighting also raged yesterday near the international airport, preventing two Jordanian passenger planes from landing, and sporadic explosions rumbled across the capital. The flight cancellations stranded many travelers, including eight Chinese construction workers who were freed by their Iraqi kidnappers this weekend.

Separately, fundamentalist Islamic leaders in Saudi Arabia are telling insurgents intent on fighting “infidels” to join the insurgency in Iraq instead of taking up Mr. bin Laden’s call to oust the Saudi royal family at home, say Saudi dissidents who monitor theological edicts coming out of the kingdom.