BAGHDAD - U.S. military deaths plunged in May to the lowest monthly level in more than four years, and civilian casualties were down sharply, too, as Iraqi forces assumed the lead in offensives in three cities and a truce with Shiite extremists took hold.

But many Iraqis as well as U.S. officials and private security analysts are uncertain whether the lull signals a long-term trend or is simply a breathing spell like so many others before.

U.S. commanders also warn that the relative peace is fragile because no lasting political agreements have been reached among the Shiite, Sunni and Kurdish communities.

Talks on returning Sunnis to the government broke down this past week, and tensions among rival Shiite parties remain high despite a May 11 truce that ended weeks of bloody fighting in Baghdad's Sadr City district.

Iraqis have experienced lulls in the past - notably after the January 2005 elections - only to see violence flare again.

"The security situation is much better than in the past three or four months, and I am making more money now," said Falih Radhi, who runs a food store in eastern Baghdad. "Despite this, I have a feeling that this positive situation won't last long and that violence may come back again."

Nevertheless, the figures for May are encouraging, especially coming as the United States continues withdrawing the nearly 30,000 reinforcements that President Bush sent to Iraq early last year to curb the wave of Shiite-Sunni slaughter.

All five "surge brigades" rushed to Iraq last year will be gone by July, lowering the troop strength to about 140,000, U.S. officials say. About 155,000 U.S. troops are in Iraq now.

At least 21 American troopers were killed in May - four in non-hostile situations. That's one more than the lowest monthly figure of the war set in February 2004.

Iraqi deaths were down, too.

At least 532 Iraqi civilians and security troopers were killed during the month, according to figures compiled by the Associated Press from Iraqi police and military reports. That's down sharply from April's 1,080 and the lowest monthly total this year, according to the AP count.

Last Sunday, military spokesman Rear Adm. Patrick Driscoll said the number of attacks in the previous week fell to a level "not seen since March 2004," though he did not give specific figures.

At the same time, Iraqi forces have taken the lead in offensives against the Sunni extremist al-Qaeda in Iraq in the northern city of Mosul and against Shiite militiamen in Baghdad and Basra in the south.

U.S. and coalition forces assumed a support role in the three offensives, enabling them to avoid higher casualties that would have been expected had they been doing all the fighting.

With the trends looking positive, the top American commander in Iraq, Gen. David Petraeus, said in Washington last week that he was likely to recommend further troop cuts in Iraq but would not promise more details until fall - as the U.S. presidential election campaign is approaching its climax.

But U.S. officials and private security analysts warned against rapid withdrawals and optimistic forecasts.

Former Pentagon analyst Anthony Cordesman wrote last week that despite some improvements among Iraqi forces, both Iraqi and U.S. officials continue "to sharply exaggerate the real-world readiness" of Iraq's army and police.

Petraeus himself said it was unlikely that Iraqi security forces could take the lead in all 18 provinces this year, as was recently predicted by the Pentagon.

"We should be skeptical about overly optimistic assessments that we've 'turned the corner' in Iraq," said Eric Rosenbach of the Belfer Center for Science and International Affairs and a former staffer of the Senate Select Committee on Intelligence.

"It's more appropriate to say that we have a long road ahead of us rather than we've turned the corner."

On Other Fronts: Blast Kills 10

A suicide bomber

blew himself up yesterday at a police checkpoint west of Baghdad, killing at least 10 people, the local police chief among them, an official said.

Fearing more

attacks, authorities imposed a vehicle ban and closed all entrances to the targeted town of Hit, in Anbar province.

The attacker

detonated his explosives belt after nearing the checkpoint, near a bridge, about 9 p.m., town administrator Hikmat Jubeir said.

Loyalists

of radical Shiite cleric Muqtada al-Sadr stepped up their opposition to a long-

term security deal being negotiated between the Iraqi government and the United States.

Senior Sadrists

urged the Iraqi government to stop the talks and hold a public referendum on the issue. Widespread opposition among the Sadrists and other Shiite and Sunni groups has raised doubts that negotiators can meet a July target to finalize a pact to keep U.S. troops in Iraq after the current U.N. mandate expires at the end of the year.

- Associated Press