Sgt. Wade Engelson is preparing his new recruits for war.

Dressed in fatigues, sporting buzz hair cuts, the new men are being trained in the use of submachine guns, explosives and chemical weapons. They have at their disposal a helicopter and, soon, an armored personnel carrier.

Engelson's men are not Navy Seals or Army Rangers. They are members of the Fresno Police Department, whose enemy will not be found in faraway lands but in the neighborhoods where the police routinely patrol -- fully armed and in urban camouflage.

In their expanding strength and mission, the SWAT team in Fresno mirrors a growing trend in U.S. law enforcement -- the rise in the number of police paramilitary units across the country and a rapid expansion of their activities, a controversial trend that police scholars refer to as "the militarization" of civilian police.

The explosive growth and expanding mission of SWAT teams has, in turn, led to complaints that an occupying army is marching through America's streets -- that they are too aggressive, too heavily armed, too scary -- and that they erode the public's perception of police as public servants.

"It's a very dangerous thing, when you're telling cops they're soldiers and there's an enemy out there," said Joseph McNamara, former chief of police in San Jose and Kansas City who is now at the Hoover Institute at Stanford University. "I don't like it at all."

In a new study, police researcher Peter Kraska and his colleagues have documented the explosive growth of SWAT, which stands for Special Weapons and Tactics. In a nationwide survey of 690 law enforcement agencies serving cities with populations with 50,000 or more, the researchers found that 90 percent now have active SWAT teams, compared with 60 percent in the early 1980s.

Even in rural communities and smaller cities, the researchers have found that two of every three departments now boast a SWAT team -- a phenomenon Kraska compares to "militarizing Mayberry," he said referring to the fictional small town in the Andy Griffith television show.

Yet more important than the raw numbers, Kraska says, the SWAT mission has expanded. Once limited to highly specialized actions, such as dealing with barricaded gunmen or hostage-takers, the SWAT teams are now increasingly engaged in more standard police work. There is a boom in "high risk warrant work," including "no-knock entries." The work is mostly related to the war on drugs, and by extension, "gang suppression."

"Where the SWAT teams were once deployed a few times a year, they are now used for all kinds of police work -- dozens of calls, hundreds of calls a year," said Kraska, a professor of police studies at Western Kentucky University. "In SWAT units formed since 1980, their use has increased by 538 percent." And some units, like those in Fresno, are being deployed full time as roaming patrols.

The 30 members of Fresno's Violent Crime Suppression Unit now patrol crime-ridden neighborhoods day and night, serving warrants at homes of suspected drug dealers and criminals, stopping vehicles, interrogating gang members, showing a presence.

As they move through the city of 400,000 people, they wear subdued gray-and-black urban camouflage and body armor, and have at the ready, ballistic shields and helmets, M17 gas masks and rappelling gear. More equipment is carried in a mobile command SWAT bus that roves the city. The deparment is purchasing an armored personnel carrier.

The tactical police here also carry an assortment of weaponry denied the normal beat cop -- battering rams, diversionary devices known as "flashbangs," chemical agents, such as pepper spray and tear gas, and specialized guns, including assault rifles and, most famously, the Heckler and Koch MP5, the short, highly accurate 9mm, fully automatic submachine gun used by the Navy Seals.

While the phenomenal rise in SWAT work has drawn some fire, police officials say the change has been a necessary one that has helped fight crime.

Fresno Police Chief Ed Winchester says that a highly armed and more violent criminal class requires an extreme response. Fresno formed its SWAT team in 1973, about a decade after the first such unit appeared in Los Angeles. Its creation occurred after an officer was shot and killed by a robbery suspect following a chaotic police response in which patrol officers fired hundreds of rounds at the suspect, borrowed an armored car and let fly canisters of tear gas, which then floated across the neighborhood.

"It was what we would call a fiasco," Winchester said, and convinced everyone that a more highly trained, specialized and disciplined unit was required.

From 1973 until 1994, Fresno's SWAT team operated only in response to very specific call-outs, such as barricaded suspects. But by late 1994, Fresno was experiencing a crime wave. There were 55 shootings in five months, with 13 people killed, including three children.

And so Fresno's traditional SWAT unit transformed itself into the Violent Crime Suppression Unit and took to the streets in constant patrols.

"The criminals aren't stupid," Winchester said. "They see eight guys surrounding them, all carrying submachine guns and wearing black fatigues, they don't want to get killed."

Fresno SWAT member C.D. Smith, writing in Police magazine in 1995, put it this way: "The streets of Fresno have become a war zone for cops, who find themselves in the heat of battle with the bad guys at least once a month."

Winchester credits the unit, in part, with reducing violent crime in Fresno by 8.7 percent in 1995 and 3.5 percent in 1996. Now, he is expanding the unit again -- for day patrols as well as night.

"Is there a downside? Sure there is," Winchester said. "It's a sad commentary -- sad when crime is so bad you got to put a SWAT unit on the street."

Yet critics warn that the growing use of paramilitary-style police units threatens the very idea of a civilian police force -- just as many law enforcement authorities begin to apply a new technique known as "community policing," putting more beat cops on the street and letting them interact more with citizens to solve problems and well as crimes.

"Despite the conventional wisdom that community policing is sweeping the nation, the exact opposite is happening," said McNamara. "The police and their communities ought to think seriously about this. Is there a need for SWAT teams? Yes, for highly specialized functions. But the police love these units, and this is a disastrous image to project."

McNamara and other police scholars say that the positive impact of the SWAT teams on reducing crime is most likely short-lived -- and that the pressure must be maintained. They also fear that heavily armed, commando-style police -- if they remain in a neighborhood for long -- will eventually be seen as an occupying army.

Kraska said his research shows that the rise in SWAT activities has closely followed the increased resources applied to fight illegal drug use.

"The drug war created the atmosphere for this kind of pro-active policing," Kraska said. "We have never seen this kind of policing, where SWAT teams routinely break through a door, subdue all the occupants and search the premises for drugs, cash and weapons."

Between 1980 and 1995, for example, Kraska found that SWAT units were employed in their traditional roles only for a minority of call-outs. Some 1.3 percent of their work was to quell civil disturbances; 3.6 percent for hostage situations; 13.4 percent for barricaded individuals. But 75 percent of their mission is now devoted to serve high-risk warrants, mostly drug raids.

Police chiefs and SWAT officers defend the practice, saying they are more aggressively rooting out and arresting drug dealers. And because of the more powerful weapons used by gangs and dealers, they say, the work should be done by highly trained SWAT teams.

Fresno Police Chief Winchester says that the SWAT teams, because of their training and style of assault, actually fire fewer shots. "They overwhelm suspects," the chief said. "They don't need to shoot."

Kraska's survey of police departments finds many SWAT teams are instructed by active and retired U.S. military experts in special operations. The SWAT teams also receive training not only from the FBI, the Federal Law Enforcement Training Center and National Tactical Officers Association, but in classes organized by private companies.

One of the most popular courses is offered by Heckler and Koch, which trains hundreds of SWAT officers a year. The company also offers the units discounts on its popular weapons, such as the MP5. Kraska points to the private companies role in the encouragement of SWAT response as part of a new "crime control industry."

Larry Glick, executive director of the National Tactical Officers Association, said that some of the private training seminars are taught by "retired military personnel who don't know what they're doing." The training offered by Heckler and Koch is "very successful and credible, among the best," he said. "Their ultimate goal is to sell their guns."

Kraska and other police scholars said that even with the most community-sensitive training, the new weaponry and paramilitary-style tactics of the SWAT units attract a different kind of officer -- less the cop as social worker and more the cop as an elite special ops' soldier. And most SWAT officers are paid a premium for the work.

"The SWAT teams love this stuff," Kraska said. "It's fun to fire these weapons. It's exciting to train. They use simmunition' -- like the paint balls and play warrior games. This stuff is a rush." CAPTION: Member of Fresno Police Department SWAT team, which patrols the California city fully armed and in camouflage, moves into position with an automatic weapon. CAPTION: Fresno SWAT team member detains a suspect during a sweep of downtown.