Twenty-five years ago they were cult heros, roaring along the nation's highways in filthy denims and leather jackets, tattooed, flaunting swastikas, mocking accepted social values. After they were glorified by Marlon Brando in the 1954 film "The Wild Ones," motorcycle gangs became firmly entrenched in the American subculture as a symbol of youthful rebellion.

Today, federal law enforcement agencies speak of "outlaw gangs" and consider them a new form of organized crime, second only to the traditional organized crime families.

Dana Caro, deputy assistant director of the FBI's criminal investigative division, compares the outlaw motorcycle gangs' current stage of development to La Cosa Nostra in the 1920s and 1930s, in the days of Al Capone.

D. Lowell Jensen, head of the Justice Department's criminal division, says that the outlaw gangs are now classified as a form of non-traditional organized crime. They are "multi-state, large scale organizations, not small organizations," he says. "We're not dealing with a handful of people. Their size is comparable to traditional organized crime . . . they're just not as effective yet."

"In parts of the country, motorcycle groups represent the true organized crime threat," he says. This is particularly true in parts of the South, Midwest and northern California, where there is little traditional organized crime activity.

"In some areas of Canada, law enforcement officials say they gangs are the law . . . they are a major power," Caro says.

Sean McWeeney, head of the FBI's organized crime division, says there is evidence that gang members have been involved in murders, drug dealing, extortion, robberies, burglaries, prostitution, pornography, loan-sharking, kidnaping, and serious firearms violations. There also is evidence gang members may be acting in some areas as subcontractors for organized crime families, even as hired killers, he adds.

Authorities say that what gangs lack in experience and sophistication, they make up for in their enthusiasm for violence. Some gangs are tightly knit operations, dependent on crime for their living, operating under a code of silence, according to law enforcement officials.

The FBI estimates that there are 600 to 800 motorcycle gangs in the country, not to be confused with the more than 100,000 Americans who are sport motorcycle riders. The FBI believes that many of the smaller gangs are involved in criminal activity as farm clubs and subcontractors for the large outlaw gangs.

Caro says that until recently, the FBI had no idea of the extent of the problem. Crimes related to motorcycle gangs were treated in piecemeal fashion, generally left up to local law enforcement.

But last year, the FBI, in cooperation with the U.S. Drug Enforcement Administration, the federal Bureau of Alcohol, Tobacco and Firearms, state and local police departments, and the Royal Canadian Mounted Police, begun a major investigation of the four largest gangs--the Hell's Angels, the Outlaws, the Pagans and the Bandidos.

Leaders of the four gangs targeted for investigation are understandably reluctant to discuss their activities. Members of the Pagans and Bandidos did not return phone calls. Larry (Mack) McDaniel, head of the Outlaws' Charlotte, N.C., chapter, refused to talk. "We don't want any publication at all," he said.

Sonny Barger, generally regarded as the national leader of the Hell's Angels, agreed to a phone interview from Oakland, Calif. He said federal law enforcement authorities are all wrong about the outlaw gangs, starting with the law enforcement charts that place him at the top of a vast international criminal empire.

"They've drawn a family tree with a little square at the top that is supposed to be me. But that's not the way it is. There is no top. This is a democracy."

"If you want to find organized crime, you're in the right place Washington D.C. ," he said. "People like DEA, ATF, they talk about how bad and rotten the Hell's Angels are. Then they break down people's doors, ransack their houses, find out they're in the wrong place and leave without even apologizing.

"DEA and ATF on their best days would make the Hell's Angels look like a bunch of Boy Scouts on a Sunday picnic," Barger said.

Barger is 43 now and has been a member of the Hell's Angels for 25 years. He believes he has taken his share of harassment from police.

He recently spent more that a year in jail on charges of which he eventually was acquitted. The government was trying to convict Barger and 17 other Hell's Angels under the RICO (Racketeering Influenced and Corrupt Organizations Act) statute, a law used primarily to go after mobsters who have infiltrated legitimate businesses and labor unions.

But Barger has served time off and on over the past 15 years on assault, narcotics and weapons violations.

He says the group as a whole is not involved in organized crime, although individuals could be involved in crimes without his knowledge. Asked about police reports that members have been involved in contract murders, he said he was not aware of any murders, but he added, "I can't say some members haven't done that. I don't know."

"In the '60s we got a lot of publicity. It was all fun and games. In the 70s, we all became gangsters. Now the DAs are all trying to make a name for themselves," he said. "We make good publicity. Whenever they can lock me up, it's big headlines."

James Stewart, a special assistant at the Justice Department, disagrees. Until recently, Stewart was chief of detectives for the Oakland Police Department. He was one of the police officers overseeing the exploits of Sonny Barger and his companions in a compound of houses on a dead-end street, surrounded by cyclone fences topped with barbed wire and patrolled by dobermans.

"These guys are not a bunch of kids on motorcycles. These guys are mature people, good organizers, good managers. They're not the ragtag group they may look like. They're not romantic Robin Hoods. In a group, they're vicious people," he said.

Over the past several months, law enforcement officers across the country have made major strikes against members of the targeted gangs:

* Last November, a task force of federal, state and local law enforcement officers raided a Hell's Angels clubhouse in San Diego and confiscated machine guns, shotguns, more than 50 handguns, explosives, bomb manuals, torture kits, electronic eavesdropping equipment, police radio scanners and narcotics.

* On Nov. 23, another cache of weapons stockpiled by the Hell's Angels was seized in Cleveland. This one included an anti-tank rocket, hand grenades, a supply of dynamite, an M16 rifle, two submachine guns, shotguns and an automatic pistol.

* On Dec. 30 in Omaha, Neb., members of the Hell's Angels were convicted of a variety of charges in connection with their efforts--including murder and torture--to corner the Omaha drug market.

* And in Tampa, Fla., in December, five members of the Outlaws were convicted in an interstate prostitution ring.

Guns seized in the raids are being traced to see if they match up with unsolved murders all over the nation.

There are reports that members of the Pagans, an East Coast-based gang, may have been involved in the bombing death of Philip (Chicken Man) Testa last year in Philadelphia. Testa was in line to head the organized crime family of the late Angelo Bruno.

"Pagans control the pill traffic. Some say Philadelphia is the pill capital of the East Coast," McWeeney said. "There's so much money involved that the Cosa Nostra has gotten involved. They want to absorb it. They're meeting some resistance from the Pagans. It has not evolved into full-scale warfare, but it could happen."

Gil Amoroso, a DEA agent from Philadelphia, said that in most parts of the country, the gangs are not yet ready to take on the organized crime families. "The family is still number one. I don't think any motorcycle club, with the exception of maybe the Hell's Angels, I don't think any East Coast Club is in a position to argue with organized crime."

But he adds, "They are dangerous in every sense of the word . . . . They're potent, they have as many people, they're a tight-knit organization. They just aren't as sophisticated--yet."

James Oppy, who is overseeing the investigation of the gangs for the FBI, says they are now channeling their money into a number of ostensibly legitimate enterprises including catering businesses, motorcycle shops, go-go bars, junkyards and massage parlors. There is evidence that the Hell's Angels, the largest and most powerful of the gangs, maintains secret Swiss bank accounts, according to federal law enforcement sources.

But asked if he has a secret Swiss bank account, Barger laughs. "I wish I did," he says. "When they show me mine, I'll split it with them."

There is more to their stance than a wistful yearning for acceptance in a world they never made. Their real motivation is an instinctive certainty as to what the score really is. They are out of the ball game and they know it. Unlike the campus rebels, who with a minimum amount of effort will emerge from their struggle with a validated ticket to status, the outlaw motorcyclist views the future with the baleful eye of a man with no upward mobility at all . . . the Hell's Angels are obvious losers and it bugs them. But instead of accepting their fate, they have made it the basis of a full-time social vendetta. -- Hunter Thompson, "Hell's Angels," 1966

There has been little academic study into why bikers choose a life-style of grease-caked levis, sleeveless vests, tattoos, swastikas, skulls, and a litany of obscene rituals mocking traditional social values.

Law enforcement files indicate motorcycle gangs started in California in the 1940s just after World War II, when groups of veterans had trouble settling down into civilian life and turned to motorcycles as a form of recreation providing a kind of quasi-military camaraderie.

One of these groups was the POBOB's (P----- Off Bastards of Bloomington) who eventually became the Hell's Angels. In 1946, following the arrest of a POBOB's member for fighting in Hollister, Calif., a group of 750 motorcyclists descended on the town to demand his release. When authorities refused, they tore the small town apart.

Throughout the 1940s and 1950s, the Hell's Angels and other motorcycle gangs became a symbol of the rebellious, less conventional younger generation. After "The Wild Ones," they were here to stay.

Roger Davis of the FBI, who has studied the psychology and behavior patterns of motorcycle gangs, says most outlaw members come from white, lower class and lower middle class families. He says many are psychopaths virtually obsessed with proving their masculinity.

"They are unconcerned with others. They don't really have a lot of feelings of conscience, a lot of anxiety about what they do. But they need a lot of ego support," which they get from fellow gang members in return for their violent behavior.

Davis says most of the women associated with the gangs are attracted when they are very young and may then discover they have no place to turn. "They stay out of fear--that they'll be hurt if they try to leave--or because they have no place to go. Some seem to have almost the same personality traits as battered women," he says.

Authorities say the willingness to use violence has contributed to the success of outlaw gang members as criminals.

There is evidence that they have been stockpiling enough weapons to fight a full-scale war, according to investigators. A favorite weapon is a .50-cal. machine gun that the gangs mount inside so-called "war wagons," vans that are used to transport weapons, drugs and money.

Amoroso says that keeping witnesses alive has been a major problem. "The bikers have an intelligence system that is probably better than most law enforcement agencies." He says that even though two gangs may be at war with each other, they will work together in hunting down witnesses.

Gangs require a code of silence and, it is difficult for someone to leave one once he has joined. The 1980 Pennsylvania Crime Commission report on organized crime points to the case of Ralph (Lucifer) Yannotta, who tried to leave the Pagans in 1973. He was taken to a quarry, injected with a hypodermic needle filled with sulfuric acid, stabbed dozens of times and shot in the head. He survived, and went on to join the Outlaws. His wife and brother-in-law were later murdered; no charges have been brought.

Because gangs are so secretive, law enforcement authorities can make only rough guesses about the membership of the major gangs, but they believe they compare in size to the traditional organized crime families. Here is a breakdown:

* The Hell's Angels, the oldest and largest of the gangs, is believed to have 4,000 to 5,000 hard-core members along with an unknown number of followers and wives and girlfriends who also participate in their activities. They are concentrated on the West Coast, but have been expanding across the country into New England, New York, Cleveland, Omaha and Minneapolis. They also have chapters in Canada, Europe, Australia and New Zealand.

* The Bandidos, with headquarters in Corpus Christi, Tex., have an estimated 2,000 to 3,000 members and are the dominant gang in most of the Southwest, with chapters in the Pacific Northwest.

* The Outlaws, with about 2,000 hard-core members, have headquarters in Chicago, with chapters throughout the Midwest, as well as along the East Coast and in Canada.

* The Pagans, organized in 1959 in Prince George's County, have headquarters on Long Island and about 2,000 members along the East Coast, especially in Maryland, Virginia and Pennsylvania.

A confidential DEA report says, "Outlaw motorcycle gangs are involved in virtually every conceivable criminal activity, not least of all drug trafficking . . . outlaw motorcycle gangs are believed to control the entire methamphetamine market. Nationwide, they could be in control of up to 50 percent of the illicit methamphetamine distribution system."

Law enforcement sources say that all over the country the major outlaw gangs are recruiting, attempting to absorb smaller gangs and becoming more professional in their criminal activities. But because new recruits are forced to commit crimes as part of their initiation, police have found the gangs impossible to infiltrate.