Associated Press Writer

From the fighting in Basra and other Iraqi cities, U.S. commanders already have hints of what to expect when their troops get to Baghdad: armed resistance from guerrilla bands, many in civilian garb, staging hit-and-run attacks, with civilians sometimes trapped in the crossfire.

U.S. plans for the battle of Baghdad are a closely held secret, but training before the war included drills in mock urban neighborhoods in Kuwait.

Urban combat is as old as war itself _ and it's a nightmare scenario fraught with special perils for any army attempting to capture a large, populated area. Some experts say an army fighting in the streets should expect to lose about a third of its force in killed, wounded and missing.

"Attack cities only when there is no alternative," Sun Tzu cautioned in his classic 5th century BC treatise, "The Art of War."

In September, the U.S. Joint Chiefs of Staff issued a study on urban combat, calling it "the most difficult and costly type" of operation, one that has "historically extracted a terrible price on attacker, defender and noncombatant alike."

During World War II, the Soviet defenders of Stalingrad outlasted a powerful German army in a ferocious 1942 siege that doomed Hitler's eastward conquest. Later, American and British troops captured city after city in the grueling victory dash across western Europe _ some easily, others not.

In the Korean War's major urban battles, U.S. and South Korean forces lost Seoul to invading North Koreans in June 1950 and then took it back three months later. While overall American casualties were not massive, one company of the 5th Marines lost 176 of its 206 men in the recapture.

Urban combat came to Vietnam during the communists' 1968 Tet Offensive, in which guerrilla units attacked dozens of South Vietnam's cities and towns, expecting to trigger a popular uprising against the Saigon government.

That did not occur, but damage and casualties were extensive. Street fighting raged in Saigon; Ben Tre became the city "destroyed in order to save it"; and Hue was ruined in a monthlong siege by U.S. and government forces to recapture the Citadel, the seat of Vietnam's imperial past.

Every such battle provides lessons for future forces. In World War II, at Hue, and in Beirut's civil war in the mid-1970s, attackers discovered that reducing masonry buildings to rubble effectively creates even better fortresses and outposts for enemy snipers.

In a 1998 symposium on urban warfare, generals Ernest Cheatham and George Christmas, who led Marine units at Hue, said the battle taught the need to visualize a tactical situation as the enemy sees it and to use bullets with "less ricochet" to protect friendly troops and civilians. They also found that ordinary tourist maps from gas stations are better for urban warfare than highly detailed military maps.

"Both generals emphasized that urban tactics … must be very flexible to meet a constant change in the close quarter combat situation," a report on the symposium said.

Perhaps most instructive for Central Command's Baghdad planning is the 1992 battle of Mogadishu, Somalia, a debacle that killed 18 Army Rangers after two helicopters were shot down.

The incident, portrayed in the book and film "Black Hawk Down," showed the extreme difficulty of putting troops into a crowded city where hundreds of armed defenders can fire automatic weapons and rocket-propelled grenades at infantrymen and vulnerable helicopters from close range.

Speaking on condition of anonymity, a military officer who is an expert in training said Wednesday that tactics have been refined since Mogadishu to avoid the mistakes made there _ one being assurances that infantry in an assault have backup from tanks, aircraft and artillery, which was not provided in the Somalia fiasco.

Military analysts say one American strategy for Baghdad envisions the use of small commando teams to carry out quick, focused missions _ such as capturing caches of weapons of mass destruction or striking at Iraq's senior leaders, including Saddam Hussein.

But U.S. planners wouldn't talk about whether the U.S. infantry and tank battalions now smashing against Republican Guard defenders outside Baghdad would be used in a classic frontal assault on the city itself.

"If we got into the situation where there was combat in the city, I'm comfortable that our forces know how to do that even though we prefer to prevent that from happening," Gen. Peter Pace, who led a Marine platoon at Hue and is now vice chairman of the Joint Chiefs, told The New York Times.

Retired Army Gen. John Abrams, who served in Vietnam, the Gulf War and Kosovo, said another component of the strategy would be an attempt to persuade Iraqi troops not to sacrifice their lives for a dictator whose tenure is short.

"We are talking about a surgical strategy against an enemy that is fortified in an urban environment," he said. "We have to do this in a way other than busting in doors … that is when the catastrophic losses begin to grow."