Troops pressed toward Baghdad with new wariness on Monday, as militiamen loyal to Saddam Hussein proved they were not a beaten force.

Iraq claimed to have shot down two U.S. helicopters and taken two pilots prisoner, a day after more than 20 Americans were killed or captured.

Saddam, in an appearance that seemed calculated to show he was at the helm, sought to rally his people Monday with a televised speech. Minutes later, Iraqi television showed images of what appeared to be a downed U.S. Apache attack helicopter sitting largely undamaged in a grassy field.

''A small number of peasants shot down two Apaches,'' Iraq's information minister Mohammed Saeed al-Sahhaf said. ''Perhaps we will show pictures of the pilots.''

The Pentagon confirmed that one helicopter was missing but offered no information about pilots. U.S. Central Command, which oversees the war in Iraq, declined comment on the footage. A military spokesman said officials were analyzing the images.

The Iraqi leader appeared relaxed and healthy on Monday - strikingly different from the way he looked in the speech aired Thursday, the day the air assault began. In full military dress, Saddam assured Iraqis ''victory will be ours soon,'' and specifically mentioned the defiant resistance of Iraqi forces in Umm Qasr, the strategic southern port that the U.S.-British coalition has struggled to hold since Saturday.

The reference seemed designed to allay any suspicion that the address had been video taped earlier, or that Saddam had been wounded or killed last week.

Saddam praised his supporters for a series of attacks Monday that inflicted the first significant casualties on the allied forces driving toward Baghdad. In one incident near An Nasiriyah, a crossing point over the Euphrates River, a group of Iraqis waved a white flag in surrender, then opened up with artillery fire. Another group appeared to welcome coalition troops, then attacked them, U.S. officials said.

Up to nine Marines died and a dozen U.S. soldiers were missing and presumed captured after the surprise engagements. Also, two British soldiers were missing after a convoy of vehicles they were traveling in was attacked in southern Iraq, British defense officials said. Additionally, two Marines were killed in accidents, military officials said Monday.

In images shown on Iraqi television Sunday, five captured U.S. soldiers - four men and a woman - appeared frightened but resolute as they answered the questions of interrogators. Arab television also showed what it said were four dead Americans in an Iraqi morgue.

''It's like a bad dream, seeing your son get captured on TV,'' said Anecita Hudson, of Alamogordo, N.M., whose son, Army Spc. Joseph Hudson, was among those captured.

Another prisoner was identified by his family as Pfc. Patrick Miller of Park City, Kan., the father of two young children.

Iraqi officials have offered repeated assurances that the prisoners would be treated humanely, according to the Geneva Conventions.

In Baghdad, black smoke poured from fires set around the city to obscure targets, hiding the sun and giving the city a bleak mid-winter atmosphere. Despite fierce bombardments early Monday, people were out in the heart of the Iraqi capital and some shops were open - mostly those selling suitcases.

Street hawkers cried for customers in the main bus terminal and hundreds of soldiers and civilians milled about. Travelers arriving from the main northern city of Mosul reported that Saddam's supporters have taken up joint fighting positions outside provincial towns and villages.

Outside An Nasiriyah, the mood among Marines was somber and tense, particularly as they learned that some of their comrades were killed while trying to take in prisoners of war. Lt. Gen. John Abizaid of Central Command said the faked surrender had sparked the ''sharpest engagement of the war thus far.''

A convoy of hundreds of vehicles snaked toward a pontoon bridge over the Euphrates early Monday, and watchful Marines lay in the sand nearby, M-16s pointed toward the desert. With many Iraqi forces discarding their uniforms in favor of civilian clothes, everyone is suspect, and all thoughts that Saddam's defenders would surrender easily have faded away.

''Clearly they are not a beaten force,'' said Gen. Richard Myers, chairman of the Joint Chiefs of Staff. ''This is going to get a lot harder.''

U.S. officials did herald one promising discovery: a suspected chemical factory near Najaf. American forces were chasing down leads from two captured Iraqi generals on possible chemical and biological weapons sites, and following up on a cache of documents found by commandos in western Iraq, Myers said.

Central Command said it was premature to call the plant in Najaf a chemical weapons factory. But such a discovery would be a coup for the United States, which says its invasion is meant to rid Iraq of these types of weapons.