The unprecedented spate of suicide bombs tearing into Iraqi crowds this month suggests a change in tactics by the man the U.S. military believes is behind many of the attacks, Jordanian terrorist Abu Musab al-Zarqawi (search).

Al-Zarqawi and other terrorists appear to be launching simpler, more frequent car bombings meant to upend the handover of sovereignty to an Iraqi regime by the U.S.-led coalition, a U.S. official said.

The relentless string of bombings — averaging one per day in June — have already killed at least 100 people and have cloaked the Iraqi capital in a mood of collective dread.

Many expect far more bombings before power is handed over on June 30.

U.S. Army intelligence has reported to U.S. combat units that insurgents may have rigged as many as 250 car bombs to be launched in an offensive expected to build to a fiery crescendo as the month draws to a close, said a U.S. military officer, speaking on condition of anonymity.

Al-Zarqawi's network, which U.S. and Iraqi officials regularly blame for suicide bombings, may be dropping its preference for complex, cataclysmic bombings in favor of frequent attacks on smaller, softer targets.

The official, who spoke on condition of anonymity, said Thursday's car bomb appeared to fit that pattern. A car bomber blew apart a crowd of Iraqi military jobseekers, killing at least 35 people and wounding at least 138.

Iraq's interior minister, Falah Hassan al-Naqib, linked al-Zarqawi to the attack and accused foreigners of being behind the 20 car bombings that have shaken the country since the start of June. He offered no new evidence.

"It may be the largest number of vehicle bombings we've ever seen in such a short period of time," said Ben Venzke, a terrorism analyst in Alexandria, Va.

Al-Zarqawi, 36, who some have linked to Al Qaeda (search), has claimed responsibility for numerous blasts over the past year, including a detonation in Baghdad on Monday that killed five foreign contractors and eight Iraqi bystanders.

Some Iraqis are fleeing the capital, saying the U.S. occupiers and the incoming Iraqi government are unable to protect them.

"Hundreds if not thousands of Iraqis are leaving," said Ismael Zayer, editor-in-chief of Baghdad's Al-Sabah Al-Jedid newspaper. "They're going to the Gulf, to Jordan, Turkey, Kurdistan, to Syria even. It's much better than losing your life for nothing. No one knows what will happen even in the next few hours."

Al-Zarqawi's alleged role came to the fore in February, when U.S. officials released a letter the Jordanian apparently wrote to the Al Qaeda leadership. The letter claimed responsibility for numerous bombings in Iraq.

Some suspect the Bush administration overstates the Jordanian's role because his presence lends credence to the administration's statements that Saddam Hussein had ties to Al Qaeda through al-Zarqawi. Many don't believe such links ever existed.

This month, there already have been six major bomb attacks. The worst previous month this year was February, with three major bombings.

The stepped-up bombings may stem from the fact that huge blasts attributed to al-Zarqawi's network have failed to derail the upcoming handover of sovereignty from the U.S.-led coalition to an Iraqi government.

Smaller bombings are easier to coordinate, allowing terrorists to intensify the campaign of intimidation aimed at Iraqis working with the coalition, the U.S. official said in a background briefing. Even small bombings appear to attract high levels of news coverage, splashed across television screens in Iraq and around the world, the official said.

The change in tactics could account for the spate of bombings in June, of which Thursday's blast carried the highest death toll.

Venzke cautioned against overemphasizing al-Zarqawi's role, saying other insurgent groups have probably taken to car bombings in Iraq, a country awash in old artillery shells commonly used in the blasts.

"It would seem that a good number of these attacks are being driven by al-Zarqawi or jihadi-type groups, but I'd be surprised if they are the only ones conducting car bombings in the run up to the handover," Venzke said.

Fewer bombings occurred in previous months, but some were far larger than Thursday's blast. In February, al-Zarqawi was blamed for twin suicide bombings that killed 109 people in two Kurdish party offices in Irbil. The following month, coordinated blasts at Shiite Muslim shrines in Karbala and Baghdad killed at least 181, mainly pilgrims.

Zayer, the newspaper editor, said he was skeptical of the incessant references to al-Zarqawi each time there is a bombing.

"It's not enough just to say al-Zarqawi, period. You have to prove it," Zayer said.

At the same time, U.S. military forces appear to be stepping up their pursuit of the Jordanian.

U.S. special operations troops are known to have moved into the Fallujah area, and U.S. aircraft last week dropped leaflets on the city urging residents to turn in al-Zarqawi.

Asked whether there is an active operation to find him in Fallujah, the official would only say U.S. forces were actively searching. "We go where the intelligence takes us," he said.

Gen. Peter Pace, speaking at the Pentagon, said there were indications al-Zarqawi might be in Fallujah. "We certainly have overwhelming military power available to be brought to bear any time we need to and want to in that city," he said.

Al-Zarqawi's network is known to have operated in Fallujah, and the military believes the Jordanian may stay there from time to time, the official said. Officials in Washington have said al-Zarqawi is thought to be moving in and out of Iraq.

Attention on al-Zarqawi has increased in recent months due in part to three recordings released on the Internet, including the video showing the beheading of American Nicholas Berg (search).

Such a profile was uncharacteristic for al-Zarqawi, who previously was not known for claiming responsibility for the numerous attacks in which he's believed to have had a hand.