Baghdad, Iraq ? Hundreds of Iraqi police and army troops fanned out across Baghdad on Thursday, setting up checkpoints and fortifying polling stations with barbed wire and blast barriers two days ahead of a historic constitutional referendum.

From the city’s Shiite stronghold of Kazimiyah to its southern approaches in the notorious “Triangle of Death,” the capital’s usually chaotic traffic was down to a tiny fraction. Many stores didn’t bother to open and others shuttered early ahead of a 10 p.m. curfew.

By nightfall, Baghdad streets were almost emptied of civilians. The large army and police presence, combined with the scarcity of people and vehicles, gave the city a disquieting calm.

Similar security precautions were in place across much of Iraq in anticipation of a spike in attacks by insurgents who want to derail the political process. Nearly 450 people have been killed in violence during the past 18 days.

Even with no people on the streets, sharp divisions over the referendum were visible in Baghdad.

Hundreds of posters and banners urging a “yes” vote were plastered on virtually every wall and shop window in the Shiite district of Kazimiyah. Iraq’s top Shiite cleric, Grand Ayatollah Ali al-Sistani, has ordered his followers to approve the constitution.

In contrast, not a single referendum poster was visible in the Sunni district of Azamiyah, just across the Tigris River.

A banner by the Sunni Arab Iraqi Islamic Party urging a “no” vote was removed from where it hung a day earlier outside Azamiyah’s Grand Imam mosque. The party changed its stance after Sunni, Shiite and Kurdish lawmakers agreed Wednesday to several amendments to the document designed to win Sunni Arab support in Saturday’s vote.

Still, no new “yes” banner was on display in the district. Many other Sunni Arab parties still oppose the charter.

In the so-called Triangle of Death, a mainly Sunni area known for kidnappings and killings, there was no sign of posters either. Iraqi troops searched cars under the watchful eyes of comrades manning machine-gun positions. U.S. helicopters hovered over the area. Traffic on the road through the “triangle” was thin.

“I will vote ‘yes’ so as to isolate the troublemakers,” said Faisal Galab, a Sunni Arab sheik from the town of Youssifiyah, about 12 miles south of Baghdad. “I have asked my family and clan to vote ‘yes.”‘

U.S. military spokesman Maj. Gen. Rick Lynch provided an upbeat assessment of the security situation ahead of the vote, arguing that the insurgent danger was far less than on the eve of the Jan. 30 parliamentary election. Also, Iraq’s security forces total 200,000 now, compared to 138,000 in January, Lynch said.

But he still expects a referendum spike in attacks.

“The insurgents have declared war on democracy and they’re going to conduct horrific acts of violence,” he said.

In a clampdown to safeguard the vote, Iraq’s borders closed Thursday at midnight and will reopen Sunday. Baghdad’s International Airport will be shut today and Saturday. Private vehicles are banned for two days starting this evening. A nationwide 10 p.m. to 6 a.m. curfew began Thursday and remains in force until Sunday.

Parliament would be next step

If the charter is adopted, a general election will be held in two months to elect a full-term parliament. If it fails, an election will still be held in December but only for another interim chamber that will try again to draft a charter.

The constitution will fail if it falls short of a simple majority or is rejected by two-thirds of voters in three of Iraq’s 18 provinces.

Underlining fears of a surge in violence, President Bush on Thursday sought to rally U.S. troops in Iraq, saying “the enemy understands that a free Iraq would be a blow to their vision. We put in motion something that can’t be stopped, and that is the march of freedom,” he told soldiers based in Saddam’s hometown of Tikrit in a video conference.

There are now 156,000 U.S. troops in Iraq, a total that has been rising in recent weeks as the 101st Airborne returns, along with lead elements of the 3rd Corps Support Command. Before that scheduled rotation, the number was about 140,000, the military said.

Security at the estimated 6,000 polling stations will be the responsibility of Iraqi police.

They will be aided by Iraqi soldiers forming a ring around polling centers, while U.S. and other coalition troops would form a wider ring, according to Lynch.

The last-minute amendments to the draft constitution adopted Wednesday were designed to win Sunni Arab support but did not meet all their demands – primarily for a clear assertion of Iraq’s Arab identity and a reduction of wide powers accorded to provincial governments that Sunnis say could lead to Iraq’s breakup.

In Fallujah, a city west of Baghdad that was once a bastion of the insurgency, local Sunni leaders met with supporters late Thursday at a mosque to get out the “no” vote.

One speaker, Sheik Kamal Nazzal, urged Fallujah mosque imams to use their Friday sermons to call for rejection.

“It’s a constitution built on sectarian bases that will fragment Iraq and divide the Sunnis,” he said. “It will not protect the rights of the Sunnis.”