In a breakthrough in the push toward Baghdad, army ground forces battled past Republican Guard units near the strategic city of Karbala and thousands of coalition troops crossed a bridge over the Tigris River. An American POW was rescued in Iraq.

As Secretary of Defense Donald Rumsfeld declared that the "circle is closing around Baghdad," American soldiers engaged Saddam Hussein's toughest troops for the first time outside Karbala, 50 miles south of the capital.

By this morning, U.S. forces had encircled the Muslim holy city and pushed farther north, Pentagon officials said.

To the east, Marines seized a bridge over the Tigris River near Kut amid fighting with the Baghdad Division of the Republican Guard, allowing Marines to cross over and push toward Baghdad from the southeast.

And in a daring raid that triggered jubilation in one West Virginian town, Pfc. Jessica Lynch, a 19-year-old supply clerk, was freed after nine days in Iraqi hands. Military officials said she was rescued from an Iraqi hospital but gave no details of the operation or her condition.

In Lynch's hometown of Palestine, W. Va., fire trucks blared horns in celebration and well-wishers crowded into the family home.

"You would not believe the joys, cries, bawling, hugging, screaming, carrying on," said Pam Nicolais, a cousin. "You just have to be here."

The developments unfolded as huge explosions rocked Baghdad, Saddam Hussein's seat of power and site of repeated bombing in the two weeks of the war. Plumes of white smoke rose from the southern end of the Old Palace on the west bank of the Tigris River, home to a camp for the Republican Guard.

Saddam - through a spokesman - summoned his country to a "jihad," or holy war, against the invaders. But American and British officials used the occasion to raise fresh doubts about the fate of a man seen in public only on videotape since the war began.

The attack on forces near Karbala marked the first major ground battle against Saddam's Republican Guard, and capped a day of aggressive American and British military actions.

Marines staged a nighttime raid on Nasiriyah, a column of amphibious assault vehicles rolling into town under a moonless sky - and finding Iraqis had abandoned a huge, walled police compound.

In Basra, a city of 1.3 million, warplanes dropped 500-pound and 1,000-pound laser-guided bombs on an Iraqi intelligence complex in an effort to dislodge die-hard defenders who have kept British forces at bay for days.

"What you're seeing today on the battlefield in Iraq is a continuation of prepping the battlefield for a major encounter with the Republican Guard," said Navy Capt. Frank Thorp.

Commanders refused to say when that might come, or whether the attack near Karbala represented the beginning of a push toward the capital. But senior American officials said the ceaseless pounding on Saddam's elite Republican Guard was taking its toll.

"Some of them have been degraded to pretty low percentages of combat capability, below 50 percent in ... at least two cases, and we continue to work on them," Gen. Richard Myers, chairman of the Joint Chiefs of Staff, said at the Pentagon.

Despite the summons to jihad issued in Saddam's name, British officials said two would-be suicide attackers had turned themselves in to troops in Umm Qasr. "They didn't want to be suicide bombers any more," said British Col. Steve Cox. "We are accommodating them."

Other British and American officials said there was a growing list of Iraqi civilians shedding their initial reluctance to assist forces fighting Saddam's regime.

Troops worked to win the trust of Iraqis, keeping in mind that many still recall promises of liberation in the 1991 Gulf War only to find Saddam's forces returned unhindered when coalition forces withdrew.

Lights went on for the first time in weeks in the port city of Umm Qasr, firmly under British control. Some British forces in southern Iraq were wearing berets in public, shedding their more warlike helmets in areas deemed safe.

Lynch, a supply clerk, was reported missing March 23 along with 11 other U.S. soldiers from the 507th Maintenance Company, based at Fort Bliss, Texas, after an ambush near Nasiriyah.

Separately, the Navy said two pilots were rescued, both in good condition, after their F-14 Tomcat crashed in southern Iraq. The plane was on a combat mission, but the crash was not believed due to hostile fire.

The American and British bombing was constant - large explosions reverberated around Baghdad - punctuated by a series of small ground engagements an a sweeping arc to the south of the capital.

A Marine official said heavy bombing was carried out around Kut, southeast of Baghdad, adding that ground forces have secured an air base farther to the south, at Qalat Sukkar, that could be used as a staging ground.