CAMP LEJEUNE, N.C. -- In remote parts of this sprawling base, Marines and sailors are training to fight on a different kind of battlefield -- an urban area where the enemy is more likely to be armed with a chemical agent or a bomb strapped to his chest than an AK-47.

In America's war on terrorism, the 4,800 members of the 4th Marine Expeditionary Brigade, reactivated Monday as an anti-terrorism unit, will be on the front line of homeland security. Wearing camouflage and gas masks, they can creep through alleys undetected, scale walls of high-rise buildings under siege and engage in combat on crowded streets.

Faced with threats of terrorism in the U.S. and abroad, all branches of the military have had to re-evaluate strategies and develop non-traditional tactics for fighting a war not just on foreign soil but in America's back yard. The formation of the Marine Corps' new anti-terrorism brigade is an example of how the Sept. 11 terrorist attacks have reshaped the U.S. military.

Assignments not set

The Marine Corps combined its three existing security guard and anti-terrorism battalions under one brigade, added an infantry unit and beefed up the brigade with an additional 2,400 personnel, the first increase of the Marines since the end of the Cold War. Though the brigade's assignments have not been decided, Brigadier Gen. Douglas O'Dell Jr., commander of the new unit at Camp Lejeune, said one-third of the brigade could be used to protect military and civilian installations in the U.S. and the remainder deployed overseas, including to American embassies and consulates.

"The world has changed since September ... and some of our training now is a little out of the ordinary," said O'Dell. The unit's training will focus on enhanced marksmanship skills and defense skills against nuclear, biological, and chemical threats, he said, as well as special training for operations in urban areas.

"It's designed to bring better deterrence, greater defense and greater detection capabilities to the Marines who are already deployed at these posts and to get them reinforcement rapidly," he said.

According to O'Dell, Marines protect 120 to 130 State Department sites around the world. Another 130 sites, mainly in locations that have been considered less vulnerable to attack, remained uncovered, he said. Now with every site under heightened alert, it is necessary to increase Marine Corps presence. In addition, the brigade could be used in case of another terrorist attack in the U.S., the general said.

Using civilian and military aircraft, rather than slower moving ships, the brigade can deploy within six hours of notification and secure a site within 72 hours, O'Dell said. The unit is scheduled to be fully operational by Dec. 1.

Troops in training

Meanwhile, 1,000 troops are undergoing six weeks of rigorous training at Camp Lejeune, combining combat skills with new techniques similar to those used by police in riot situations. In one drill, Marines wearing protective coverings rescued a mock victim from a building where sarin gas had been released. In another exercise, instructors sprayed pepper spray in the faces of infantrymen, so they could learn how to work during a chemical attack.

As the military has had to adjust to changing times, it also has had to adapt to changes abroad, according to O'Dell.

"There has been a tremendous migration worldwide from the country to the cities, particularly in coastal areas," said O'Dell. "Oftentimes those sites are located in the vicinity of airfields and port facilities that may prove useful to us as the campaign goes on."

Armed with M-16s and A-2 service rifles, Marines have been training to take control in highly populated areas where terrorists could pose the most serious threat. At the same time, the Marines are learning how to negotiate without violence and use nonlethal weapons such as foam bullets, beanbags and rubber torpedoes.

"In an urban environment, they [attacks] can come from any direction. We train them as best we can, using whatever we have, so that when they do hit, they will be as prepared as possible," said a sergeant from the 4th Marine Brigade. "It's important not to overpower a situation, to know when it is more appropriate to read a subject from their expression and talk them down if you can."

The brigade includes the 3rd Battalion, 8th Marines at Camp Lejeune, whose sister battalion was bombed in Beirut in 1983, killing 241 Americans. It also includes the Marine Security Guard Battalion, headquartered in Quantico, Va., which guards embassies and consulates around the world; the Marine Security Forces Battalion, based in Norfolk, Va., responsible for protecting Navy installations and ships; and the Chemical Biological Emergency Response Team of Indian Head, Md., a unit of 400 Marines trained to treat victims exposed to contamination. That unit, formed after the 1995 sarin gas attack on a Tokyo subway, has been involved in efforts to bring the anthrax contamination under control in Washington.

The Marines, the military's smallest service, dropped in numbers from 196,000 at its peak during the Persian Gulf war to a current 172,000 men and women. The secretary of the Navy has issued orders to delay the discharge of Marines who have served their enlistments. Several hundred reservists also have been called up. The initial added cost of the brigade is about $21 million, officials said.

`New actions' required

The new brigade is an indication of the Marine Corps' flexibility and culture, according to Marine commandant Gen. James Jones, who has had a long-term goal of creating the umbrella unit.

"As of last month, we are faced with a new reality that requires new actions on our part," Jones said during the reactivation ceremony Monday. "Our response to the asymmetrical warfare ... in this first war of the 21st Century is multifold. Part of our response to terror is standing up the 4th MEB."