WASHINGTON — The American military is training furiously and polishing a plan for attacking Baghdad that calls for isolating the city and then taking control of it by seizing or destroying Saddam Hussein's pillars of power — but avoiding house-to-house combat in its hostile streets.

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 govrnment.

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."

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.

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.

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, windows 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 tarpaulins. 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."

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