The first American foray into Baghdad was a quick in-and-out trip, by design. With more likely to come, these "pinpoint missions" are meant to show off U.S. military might and flush out Iraqi defenses.

At the same time, U.S. troops are moving to encircle the city with armored vehicles, choking off reinforcements or escape for Saddam Hussein's regime.

With fighting continuing elsewhere in Iraq, the Baghdad portion of the allied war plan swung into action on Saturday. The strategy has psychological and tactical advantages for military commanders aiming to avoid bloody urban warfare and woo the city's millions of civilians.

The "vise" closing on Baghdad that President Bush described earlier in the week continued to press from several directions.

Now, special operations forces watch the roads leading northward out of Baghdad to Saddam's hometown and power base of Tikrit. A senior U.S. military official said several key, unidentified objectives to the north and northwest also had been taken.

As soldiers who have dashed to the city's outskirts advanced closer from the southeast and southwest and worked to consolidate the coalition's hold on the main airport, columns of armored vehicles started to surround Baghad.

U.S. planes also were put on 24-hour alert overhead, to provide close air support for any ground invasions.

Then there was the bold daytime raid into southwestern portions of the Iraqi capital, in which a reconnaissance force of tanks and armored vehicles from the 3rd Infantry Division rumbled through the streets and back out west again toward the airport.

A U.S. official familiar with military planning termed such operations "pinpoint missions," not meant to establish a permanent toehold inside the city limits. Instead, they are a chance for the allied troops to show the flag — and will continue as opportunities present themselves, the official said.

The reason? Showing that the allied troops can go where they want, when they want, could lead to the surrender or overthrow of Saddam's government, Pentagon officials say.

"It's certainly a psychological effect where the regime leaders have continued to lose control and now they see tanks in their streets and these types of visuals, and then they see people in the military handing out food and water," said James Wilkinson, a Central Command spokesman. "That's a very big, deep and not so good psychological impact for the regime."

In addition to denting the confidence of Saddam's government, military planners hope civilians will see coalition forces are serious about toppling the regime and start providing information, said Bill Taylor, senior associate at the Center for Strategic and International Studies, a Washington think tank.

The operations also have a pragmatic, tactical purpose — searching for key intelligence about the troops and weapons inside the city.

But they come with significant risk to coalition forces of sniper attack and other ambushes, Taylor said.

Meanwhile, the pincer troop movements have create a loose cordon around Baghdad that is designed to control — but not completely cut off — traffic in and out of the city. Civilians will be allowed out and humanitarian aid in, Pentagon officials said, while supplies will be kept from Iraqi troops fighting outside the city and reinforcements prevented from entering.

"We don't want a classic siege. We can't have a classic siege, because of the civilians," Taylor said.

Encircling the city also creates a sort of standoff, he said. U.S. officials hope that troops arrayed outside the city will draw the Iraqis out to attack, while Saddam's forces want to lure the Americans into vicious street-to-street battles.

Taylor predicted the next stage of the American plan, after a series of additional in-and-out missions, would be to fight sector-by-sector inside the city but never fully engage in the dreaded all-out urban assault.