American and British forces advanced Friday through southern Iraq, some racing unimpeded across the desert, others meeting hostile fire. Hundreds of Iraqi soldiers surrendered and U.S. officials said Iraq's command structure appeared to have disintegrated.

The allies reported their first combat casualty, a U.S. Marine killed in southern Iraq.

Twelve more Marines - eight British and four American - died when their helicopter crashed and burned in Kuwait. Officials said the crash was not caused by hostile fire.

Hoping the regime might capitulate, U.S. military commanders held back-channel negotiations with Iraqi commanders and refrained from all-out bombardment. Instead, U.S. missiles and bombs struck specific targets including the main presidential palace in Baghdad and strongholds of the elite Special Republican Guard.

Iraqi Information Minister Mohammed Sa'eed al-Sahhaf said one of Saddam Hussein's homes was hit in the bombing, though no one was hurt.

U.S. officials said they had no definitive word on whether the Iraqi leader was caught in the attack, but indicated that medical workers were summoned to a compound in Baghdad after it was hit. The officials said Iraqi forces subsequently seemed cut off from their leadership.

The official Iraqi News Agency said 37 people were injured in the latest strikes on Baghdad, and Iraqi military said four soldiers were killed. There were no figures given on Iraqi losses in ground combat.

Thousands of American anti-war activists protested, blocking streets, boycotting classes and chaining themselves together. More than 1,500 people were arrested, mostly at a raucous demonstration in San Francisco.

U.S. and British forces moved on a broad front, with infantry racing across the desert in thousands of tanks and trucks, plumes of dust in their wake, and Marines edging cautiously toward strategic oil towns and military outposts, calling in air support to take out snipers. In some cases, units were preceded by special forces teams.

Capt. Al Lockwood, spokesman for British forces, said the U.S.-led attack could reach Baghdad swiftly.

''If I was a betting man, and I'm not, I would say hopefully within the next three or four days,'' he said.

In western England, American B-52 bombers began taking off from a British air base. Officials refused to disclose their mission; they would be capable of reaching Iraq in about six hours.

U.S. Marines seized a portion of the main road leading from Kuwait to the city of Basra, suppressing resistance from Iraqi mortars and arms. Officers said the seizure could help speed the takeover of Basra, southern Iraq's largest city.

Another Marine unit, the 7th Infantry's 3rd Battalion, had to delay its foray into Iraq after it was reported that numerous tanks were sighted unexpectedly on the Iraqi side of the border.

The unit took small-arms and artillery fire Thursday night, and at one point a U.S. Cobra helicopter accidentally fired a missile at an American tank, injuring one soldier and forcing abandonment of the smoldering tank.

Within a few hours of crossing into southern Iraq, the 15th Marine Expeditionary Unit encountered 200 or more Iraqi troops seeking to surrender.

One group of 40 Iraqis marched down a two-lane road toward the Americans and gave up. They were told to lie face down on the ground, then were searched by Marines.

Waving Iraqi civilians greeted members of the 1st Marine Division as they entered the town of Safwan.

''We're very happy… Saddam Hussein is a butcher,'' said a man in the back of a pickup truck, identifying himself only as Abdullah. A woman fell at the feet of the Americans and embraced them, touching their knees.

Soldiers from the Army's 3rd Infantry Division also crossed into Iraq and encountered several Iraqi armored personnel carriers, destroying at least three, troops reported by radio. British troops moved on the strategic al-Faw peninsula - Iraq's access point to the Persian Gulf and the site of major oil facilities.

Iraqi troops set fire to 30 of the hundreds of oil wells in the region, British Defense Secretary Geoff Hoon said. Iraq has 1,685 oil wells and exported 2 million barrels daily before the war.

In Washington, the Senate unanimously approved a resolution in support of U.S. forces. The House approved a similar measure early Friday on a 392-11 vote after sometimes angry debate. Some Democrats said the Republican House leadership was forcing them to offer ''unequivocal support'' of President Bush.

Divisions over the war were stark in numerous cities across the country, anti-war protesters took to the streets and in some cases were confronted by counter-demonstrators. ''Support the U.S. or keep your mouth shut,'' said one sign in Mississippi.