Just two months ago the Pentagon's public message to Iraqi leaders was sharp and loud: Our patience is thinning, the clock is ticking.

But as Defense Secretary Robert Gates returned Saturday from his fourth trip to Iraq in seven months, he appeared to take a softer tone, and a more wait-and-see approach.

While U.S. leaders are still expressing frustration that the Iraqi government is not moving fast enough to enact political reforms that are hoped to temper the violence still raging, there is a sense that the message has been delivered, and any more pressure could do more harm than good.

As he wrapped up his brief stop here, Gates talked about the challenges faced by the Iraqis as they struggle to patch together their fragile democracy, and he noted that change comes slowly.

"No country can escape its history," he said. "The reality here is the Shia were repressed for a long time, as were the Kurds. Sadaam Hussein and most of those in his government were Sunnis ... To try to bring these three groups together along with other minorities in Iraq is a difficult endeavor."

Gates' visit coincided with a broad security lockdown in Baghdad, as Iraqi leaders imposed a strict curfew after the bombing last week of a sacred Shiite shrine north of the city. Early last year a similar devastating bombing there plunged the country into explosive sectarian strife, which has continued into this year.

As Gates left, and the city prepared to lift its curfew, U.S. officials held their breath.

They were unsure whether the swift actions by political and military leaders to urge calm, shift troops around, and protect other threatened locations diffused the situation or merely delayed the inevitable backlash?

"The fact that we have not seen the kind of violent reactions develop yet that we did in February 2006 is worth noting," U.S. Ambassador Ryan Crocker said. And Gen. David Petraeus, the top U.S. commander in Iraq, told reporters traveling with Gates that while the "situation is still very tense and sensitive, it appears that this united leadership of Iraqis from all parties has in fact, helped to bring about restraint."

Still as military leaders huddled with Gates, there also are no signs that U.S. commanders have backed away from recent suggestions that they may need to maintain the latest buildup of forces into next year to give the Iraqis the time they need to show they can take control of their own country's security.

It's a message Congress is not likely to receive well.

The Democratic-led House and Senate are unwilling to wait much longer for the U.S. to extricate itself from Iraq.

Lawmakers have set a list of benchmarks they want the Iraqis to hit in coming months, and the Pentagon has to give Congress a much-anticipated assessment of the Baghdad security plan in September.

With those pressures mounting, the U.S. military launched what members of Congress could view as its final, desperate push. Armed with nearly 30,000 additional troops, U.S. forces started a broad offensive aimed at rooting out Al Qaeda from the outlying Baghdad neighborhoods.

In announcing the newest campaign Saturday, Petraeus said that U.S. forces are moving into key Al Qaeda sectors where they have not been able to penetrate well before.

There are areas, he said, "where we still have some significant work to do, to insure the fault lines do not once again produce a spiral of violence that can be so damaging."

And with more U.S. troops engaging the insurgents on their own turf, there are prospects for more American casualties. It will get tougher before it gets easier, Petraeus warned again.

There are a few fragile wisps of hope, but Gates and others were hesitant to tout them too loudly for fear the progress would stall once again, or get swallowed up in a new surge of sectarian killings.

Car bombings in Baghdad have been dipping steadily, Petraeus said, and sectarian murders — which increased in May, have declined again, to a level of about one-third what they were in January. U.S. and Iraqi troops, scattered across the city in neighborhood security posts, are getting more tips, that lead to the capture of insurgents and discovery of weapons caches.

But at the same time, some negative signs continue.

The U.S. is coming off one of its most deadly months in the five-year war, pushing total American deaths past 3,500. Insurgents continue to improve their assaults, developing more sophisticated and deadly roadside bombs, and burying them deeper into the ground with multiple trigger wires.

And Iranian-made weapons are still finding their way into Iraq, suggesting that outside influences continue to drive more violence.

Still, as Gates headed for home, he offered a hint of optimism.

"We understand that there are a number of things that are reasonably close that with some will on the part of the different parties could be accomplished," Gates said, adding that his goal was to encourage Iraqis to make that progress.