The new strategy is a significant change in Pentagon doctrine. In World War
II, the American military dealt with the difficult question of urban combat
by using heavy artillery, intense fire-bombing and, twice over Japan, even
atomic weapons. Since the war, the strategy had been to isolate urban areas,
then move on to other targets.

Today, commanders still say they would rather avoid fighting in Baghdad and
other Iraqi cities, which could result in thousands of American casualties
and even more civilian deaths. But now, with Republican Guard units digging
in around Baghdad, they may have no choice should Mr. Hussein and his
die-hard adherents choose to make a last stand.

If they must fight there, American generals say, they will choose their
targets carefully and try to overwhelm them with such decisive force that
the Iraqis' will to fight collapses.

To that end, marines are training in new mock cities on military bases on
Guam and in southern California. At an Army training center in Louisiana,
more than 3,000 soldiers from the 10th Mountain Division, based at Fort
Drum, N.Y., prepared today for an overnight attack Tuesday on another fake
city.

At the same time, intelligence agencies are rushing to update military maps
using high-resolution satellite photographs, military officials say. They
have also asked foreign construction companies for blueprints of the palaces
and ministry buildings they built for Mr. Hussein.

In just the past few years, the whole American doctrine of urban warfare has
changed. Where the strategy had been either to avoid cities or to destroy
them, under the new doctrine the Pentagon's goal would be to isolate the
cities, then selectively attack the pillars of the government. Fighting
block by block is considered too risky and too likely to cement popular
defiance. Rather, the military hopes Mr. Hussein's government would implode
as he loses control over his loyalists.

That approach requires accurate intelligence, tight coordination and rapid
movement by the attacking forces. It also calls for faith that civilians
would welcome their "liberation," as Defense Secretary Donald H. Rumsfeld
has suggested.

Even if Baghdad fell, a bloody urban battle with a high civilian toll could
be seen as a political failure for the Bush administration — at home and
throughout the Middle East.

Senior military officials say American troops are prepared to fight and win
in the cities of Iraq, but they are planning on ways to avoid that kind of
Pyrrhic victory.

"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," said Gen. Peter Pace, vice chairman of the
Joint Chiefs of Staff, who commanded a Marine rifle platoon during the
vicious fight to oust the North Vietnamese Army from Hue in 1968.

What worries the generals is how cityscapes rob the American military of
many of its overwhelming advantages. Even guided long-range bombs can be
risky to use in dense cities. Radios often do not work. The best
surveillance equipment cannot always find enemies in alleys.

The broad details are spelled out in a document called "Joint Publication
3-06: Doctrine for Joint Urban Operations." The paper was completed just one
month ago by the Joint Staff, and incorporates lessons learned in the
American missions in Mogadishu, Somalia; Belgrade, Serbia; and
Port-au-Prince, Haiti, and in the Russian fight for Grozny, the capital of
Chechyna. [The document is online at nytimes.com/iraq.]

The "multidimensional surveillance" it calls for is already under way,
pinpointing political and military headquarters, electrical and water
supplies, food distribution centers and broadcast studios — as well as
places like mosques, embassies and Red Cross warehouses that should not be
attacked.

An attack would start with a siege, not just by troops and weapons, but by a
wall of electronic jamming. The goal is to "control the flow of supplies,
personnel and information into and within the urban area" in order to
"physically and psychologically isolate" it. There would be broadcasts and
leaflets to demoralize fighters and calm civilians; similar operations would
continue after state-run television and radio stations fell.

When and if fighters enter a city, they need "overwhelming combat power" —
not to level the city but to capture or destroy crucial targets with such
"speed, firepower and shock" that resistance collapses.

"First, you want to control all routes in and out of the city," said Lt.
Col. John Nicholson, who commanded the first of the Army's new Stryker
brigade combat teams built around quickly deployable, wheeled armored
vehicles that could spearhead an urban assault. "You want to isolate the
city. Then you want to isolate specific targets inside the city. You don't
want to take the whole city. Rather, you want to control it by destroying
some objectives and controlling others."

Political considerations play a major part in shaping the plan. "You must
have a clear understanding of the political objectives," said Colonel
Nicholson, now an aide to the secretary of the Army, Thomas E. White. "You
can't just go in and rubble a city if your goal is to quickly transition to
a post-conflict friendly government."

That is why modern doctrine sees no point in razing cities.

"You need to figure out what pieces of the city or what things you have to
attack in order to get the results you want," said James A. Lasswell, a
retired colonel at the Marine Corps Warfighting Laboratory in Quantico, Va.,
who played a pivotal role in rewriting the Marines' doctrine on urban
combat.

Complications like these are what prompt senior officers to say will avoid
urban combat if possible. The military must be ready to deal with refugees,
relief aid and civil order, including crowd control, and to get power
stations and water treatment plants up and running in parts of a city that
have surrendered or have been seized. "I wouldn't get sucked into the
cities," said Gen. Anthony C. Zinni, a former head of the Central Command.
"There would be a lot of casualties on our side, we'd kill a lot of
civilians and destroy a lot of infrastructure, and the images on Al Jazeera
wouldn't help us at all," a reference the Arabic satellite network.

Historically, military forces attacking cities have suffered 30 to 40
percent casualties in the intensive fighting. In war games, the new approach
has reduced estimated casualties to 10 percent.

At Quantico, a team of marines assigned to a study called Project Metropolis
have found that new tactics are probably more important than new technology.

Jet and helicopter pilots simulating attacks to support ground troops are
rehearsing new angles of attack, having discovered that plate glass windows
in office buildings can deflect the lasers used to identify their targets.

When four infantrymen move with a single M1-A1 tank, others can keep watch
over rooftops and other enemy outposts while the tanks provide devastating
firepower that no foot soldier can match.

Marine experts at Quantico found that it takes four or five weeks — twice
what most Army and Marine Corps infantry units spend each year training for
urban fighting — to become proficient at the new tactics. Some training can
be done at rudimentary sites, with mock houses rigged of two-by-fours and
plastic sheeting. A number of bases have complexes with 30 or so buildings
that troops quickly master.

Marines are now using a 1,000-building complex at George Air Force Base, a
shuttered installation in southern California. There, as in a strange city,
many buildings look alike. There are no street signs. Marines learn to
divide the mock city into grids, and to call in air strikes.

"We still don't have enough training facilities that put the average marine
or soldier in an urban environment," said Randy Gangle, a retired colonel at
the Warfighting Laboratory who was instrumental in developing in the Marine
Corps's new urban combat doctrine.

Old tactics, and the clichés that describe them, are being discarded. Army
and Marine ground troops do not talk so much about kicking down the doors;
too often, they are booby-trapped.

Instead, for example, they are studying how the Israeli Army, in the recent
fighting in Jenin, used specially loaded tank rounds to blast holes in the
walls of buildings. The charge is designed to open the wall, but not to
blast through the building, collapse it or hit what lies beyond.

Technology has its role. Ground-penetrating radar and heat sensors can
locate enemy fighters in tunnels or behind walls.

One such device was quietly loaned to rescue teams after the Sept. 11
attacks on the World Trade Center, Pentagon officials said. Called the
Tactical Mobile Robot, this small, remote-controlled vehicle, which is still
undergoing tests, burrows through walls or concrete and sends back pictures.

Urban operations would begin after sundown, when American optical technology
allows its forces to dominate the battlefield while many adversaries are
blinded by the night. Most residents are at home, so they do not fill the
streets. The streets are the most dangeous place.

"We expect 80 percent of our casualties would be outside the buildings and
in between," said Col. Robert L. Caslen Jr., chief of staff for the 10th
Mountain Division, whose 2nd Brigade is preparing for an urban assault
exercise this week in Louisiana. "Roads and alleys channelize your
movements, and they give a great field of fire for the enemy."

More than 2,500 years ago, the Chinese military strategist, Sun Tzu, warned
that urban combat tires troops, courts casualties and voids a victory. "The
worst policy is to attack cities," he wrote.

Today, Pentagon strategists have seen little to alter that analysis.

"If we have to fight a pitched battle in Baghdad," said one senior officer
with access to the war planners, "it means we screwed up somewhere along the
way."