BAGHDAD, Iraq (AP) – An uptick in airstrikes and other military moves point to an imminent showdown between U.S. forces and Sunni Muslim insurgents west of Baghdad – a decisive battle that could determine whether the campaign to bring democracy and stability to Iraq can succeed.

American officials have not confirmed a major assault is near against the insurgent bastions of Fallujah and neighboring Ramadi. But Iraqi Prime Minister Ayad Allawi has warned Fallujah leaders that force will be used if they do not hand over extremists, including terror mastermind Abu Musab al-Zarqawi.

A similar escalation in U.S. military actions and Iraqi government warnings occurred before a major offensive in Najaf forced militiamen loyal to radical Shiite cleric Muqtada al-Sadr to give up that holy city in late August. And U.S. and Iraqi troops retook Samarra from insurgents early this month.

Now U.S. airstrikes on purported al-Zarqawi positions in three neighborhoods of eastern and northern Fallujah, 40 miles west of Baghdad, have increased. And residents reported this week that Marines appeared to be reinforcing forward positions near key areas of the city. Other military units are on the move, including 800 British soldiers headed north to the U.S.-controlled zone.

The goal of an attack would be to restore government control in time for national elections by the end of January. However, an all-out assault on the scale of April’s siege of Fallujah would carry enormous risk -both political and military – for the Americans and their Iraqi allies.

A videotape obtained Tuesday by Associated Press Television News featured a warning by masked gunmen that if Fallujah is subjected to an all-out assault, they will strike “with weapons and military tactics” that the Americans and their allies “have not experienced before.”

Regardless of whether the threat was an empty boast, insurgents elsewhere in Iraq could be expected to step up attacks to try to relieve pressure on fighters in the Fallujah and Ramadi areas.

But the main problem an assault would pose for both the U.S. military and Allawi’s government is political, such as a widespread public backlash. A nationwide association of Sunni clerics also has threatened to urge a boycott of the January elections if U.S. forces storm Fallujah.

So Iraqi officials appear anxious to convince the public that they have made every effort to solve the Fallujah crisis peacefully. The government spin is that the people of Fallujah are held as virtual hostages of armed foreign terrorists. Although Fallujah leaders insist there are no more than a few foreign fighters in the city, Arab journalists who have visited say they heard non-Iraqi accents at some checkpoints.

U.S. and Iraqi officials hope the Iraqi people are so fed up with suicide attacks, assassinations and kidnappings – many of them believed orchestrated from Fallujah and Ramadi – that they will acquiesce to the use of force.

“There are terror groups in this city who are taking human shields,” Iraq’s deputy prime minister for national security, Barham Saleh, said Wednesday, referring to Fallujah. “We are working hard to rid the people of Fallujah of them and to let security and stability prevail across Iraq.”

In the event of an attack, Iraqi insurgents, who have skillfully used the Internet as a propaganda tool, would likely attempt to muster opposition in the Arab world with graphic accounts of the suffering and death of innocent women and children caught up in the fighting.

It’s a tactic that worked when Marines attacked in Fallujah last April seeking to root out foreign fighters and capture the killers of four American security contractors whose mutilated bodies were hung from a bridge over the Euphrates River.

The attack was called off within weeks – reportedly on orders from the White House – after a wave of outrage among Sunni Muslims in Iraq and elsewhere over reports that hundreds of civilians had been killed. Ghazi al-Yawer, now the interim president, and other leading Sunni politicians threatened to resign from the then-Iraqi Governing Council if the assault did not stop.

After the Marines pulled back, the city fell under the control of extremist clerics and their mujahedeen allies, who had defended Fallujah against the Americans. The Fallujah Brigade, organized from residents to assume security duties, melted away within a few months.

Weeks after the siege ended, Iraqi politician Ahmad Chalabi and others complained that the April agreement enabled insurgents to transform Fallujah into a sanctuary. The wave of car bombings and the beheading of foreign hostages that accelerated after the end of the Fallujah fighting seemed to validate those criticisms.

To avoid a repeat of the April political disaster, the Iraqi government has been preparing the public for a showdown. On Wednesday, Allawi said more extremists were flooding into Fallujah.

Although negotiations with Fallujah clerics broke down this month, government ministers maintain they are still in contact with community leaders in hopes they will hand over al-Zarqawi, a Jordanian whom the clerics insist is not in the city.