On the streets, Dwight Welcher robbed and stole. In jail, he raped. His motive was always the same: to win prestige.

"If I can completely destroy this person here rape him , it tells everyone I'm okay," says Welcher, 29, a convicted armed robber who says he raped several men each week while he was in the Prince George's County Detention Center in 1980 and 1981.

Welcher's values are known among jail officials as "the inmate code." This is how jail inmates define that code: The strong, violent inmates exploit the weaker, nonviolent ones. In many cases, exploitation takes the form of rape.

The idea that the strong dominate the weak is rooted in a certain concept of manhood: A man is someone who dominates others. The concept prevails among criminals who victimize the powerless. It persists in the county jail, where the nonaggressive inmates often are not protected from the violent ones, and the convicted are not always separated from the innocent.

"It's like the Christians and the lions," says a former county jail inmate, James Foley.

In the Prince George's detention center, as in many jails and prisons, inmates say they deliberately test each other to determine who is not aggressive -- and therefore a potential rape victim. The tests begin the moment an inmate enters the jail.

When a guard gives an inmate his jumpsuit, the other inmates watch him carefully: Will the new inmate insist on a new jumpsuit, with sleeves and pants that fit properly, or will he simply take what he's given? If he takes the first jumpsuit offered, the inmates mark him as passive, a possible victim.

Next the inmate enters the "holding tank" of the jail, known as 1A, a cage the size of a large living room that was designed for 20 inmates but frequently holds 80. Within one hour, the new inmate faces more tests, administered by potential rapists: Does the inmate want a cigarette? If he does, he is a potential rape victim. Experienced criminals never take that cigarette, realizing that this is a world where there is no kindness -- and where the man who takes a cigarette will be expected to pay it back with a sexual favor or be raped.

More tests: Throughout the county jail, inmates steal the property of other inmates, including sneakers, toothbrushes and meals. If an inmate is not willing to fight a fierce battle against another inmate to get his toothbrush back, he is marked as "weak" and a potential victim. If an inmate fights another inmate over his toothbrush but wages a poor battle, he is raped.

"Every fight has something to do with sex," says Denis O'Brien, a former inmate at the county jail. "You can't get knocked out. If you get unconscious, you get raped, and not just by the guy you were fighting."

Francis Harper, who says that he raped three men in the Prince George's jail, echoes O'Brien: "If someone is timid, he's going to be a victim."

Inmates say that there are several brutal fights each day in the county jail.

Some of the fights begin over the same mundane matters as fights outside of jail: territory and personal possessions. The big difference in jail is that about two fights per week result in forced anal penetration, according to guards, inmates and a jail medical technician, and at least 10 fights per week occur when inmates force other inmates to perform oral sex.

The fear of rape encourages many inmates to arm themselves with "shanks," knives that they make from toothbrushes and bed bunk posts. It also encourages many inmates to behave more violently in jail than they normally would, even raping others so that they will not be raped, according to some inmates.

Eventually, these people get out of jail, with a lot of experience in behaving violently.

The jail rapists are heterosexual men; they have girlfriends or wives; some have children. They laugh off any suggestion that they are homosexual because they rape men. Welcher's response was typical of 24 other inmates who were interviewed and said they were rapists: "In jail you're not a homosexual if you're the aggressor. You're more of a man, if anything."

Says Welcher: "It goes back to the mentality of the street, the definition of a man. On the street, a man is producing babies, having women, having sex. Sex is one of the things you identify with manhood. In jail manhood is everything because you have nothing else."

Welcher, currently serving time in the House of Corrections in Jessup, says he raped several inmates each week in the Prince George's County Detention Center in 1980 and 1981.

Unlike most jail rapists, Welcher did not beat his victims, according to Welcher and one of his victims, Ralph Bunche Gordon. Welcher's weapon was the threat of violence. Inmates in Welcher's cellblock constantly observed gang rapes and brutal beatings, so Welcher's tactic was to tell a potential victim that a group of men wanted to gang rape him. Then he would offer the victim protection, at a price: The victim would have to have sex with him and a friend or two. In most cases, Welcher says, his con worked.

"Call it high class rape," says Welcher.

Welcher's main motive was the same as that of all jail rapists: the need for prestige. Unlike many jail rapists, however, Welcher was more interested in sex than in violence.

"In jail," Welcher says, "there are no women. So you try to keep a bunch of guys who will substitute."

Welcher says that it was comparatively easy to change the sexual orientation of some of his fellow inmates. "There's a woman in every man and a man in every woman," he says. "If you want to turn someone into a homosexual you have to bring out the woman. I want to deal with the woman. I don't want to deal with the man."

Welcher says that after raping the young men he would make them become his version of women by putting them on a pedestal. "I'd tell them they're beautiful people, they're smart, I'd serve them, I'd say 'go first, this is my woman here.' You constantly redefine his whole life. He doesn't know the part he has to play, so I teach him some lines."

But there were other reasons for Welcher's scheme besides sexual desire. First: he was afraid of being raped -- and by raping others he established himself as an inmate worthy of respect. Second: "Everyone likes to dominate so you make sure there are two groups, the dominant and the not. You have to maintain that separation. You have to say he's dominant, he's gay."

Why did Welcher and his friends feel this need to dominate others?

"Because they've been dominated," says Welcher. "They been stepped on. They're poor, from the streets, from broken families. That's the way of life on the streets. But nobody wants to be at the bottom. Everyone wants to be the pimp, the stickup man. That's the only thing they relate to. They bring the same thing to jail."

Welcher and other inmates who say they were rapists express no guilt over their actions. They believe that "a real man" -- their words -- would kill rather than get raped. In their view, a man who is raped must be homosexual and therefore should not mind it.

"It could happen to me but it'd be me on the floor dead with a knife stuck in my back," says Kevin Wilson, an armed robber and former inmate at the county jail who says he participated in a gang rape there. "These people submit to it. If a man submits, he's gay."

In fact, most jail rape victims are not homosexual, according to The Post investigation. They simply are not used to defending themselves -- particularly against a group. Those who are homosexual deny that they want to be raped.

The inmate code has several other provisions. One of them is that men charged with molesting children -- or with raping women -- get raped. "It could be my little sister, or my mother, and here I am locked up," says Joseph Roberts, one admitted jail rapist. "So you do it to him to show him how it feels."

That message doesn't always get across, however. The only jail rape victim interviewed by The Post who says he is not now troubled by having been raped was a man convicted of raping a woman. The man, Ralph Bunche Gordon, 24, a former University of Maryland student, says this of his experience as a rape victim: "It just happened. I don't feel anything."

Another provision of the inmate code is that everyone hates a "snitch," someone who tells police or jail guards about another's crime. In the county jail, snitches get raped. Most inmates know this. They also know that the guards do or can do very little to protect inmates. As a result, few inmates snitch--and few rape victims report their rapes to guards.

Says Francis Harper: "Prisoners see that the guards don't help so they don't play by the institution rules. They play by the inmate rules, it's safer." THE SERIES The Post studied 24 cases of male rape and sexual assault that occurred in the Prince George's County Detention Center from 1978 through 1982.

Twelve cases were chosen to illustrate different aspects of the problem; today's stories involve the last two cases.

County jail officials, prosecutors, defense attorneys and judges say they are aware that rapes occur at the jail. But the rapes continue, hidden from public view yet with serious consequences to society.

The rapists' names were obtained through interviews with victims. Most of the rapists were interviewed in Maryland prisons where they are now incarcerated. A few, who are now out of jail, were interviewed in their homes.

The victims' names came from sources in the jail and the Prince George's County Courthouse. Those mentioned by name gave permission for their names to be used. Most were interviewed in their homes.