Each day at 6:30 a.m. the green school bus loaded with 30 Maryland prison inmates left a minimum-security pre-release center in Jessup and cruised up the Baltimore-Washington Parkway to downtown Baltimore.

The bus threaded its way through early morning traffic and at 7 a.m. the inmates were dropped off at three downtown street corners where, unsupervised, they were trusted to board public buses to take them to college classes and work sites in the city.

But during a six-week investigation by Baltimore City Police, the prisoners allegedly were discovered in virtually every section of the city except those in which they were intended to be. Show bars on the The Block. eDope dens in West Baltimore. Driving fancy, late model cars.

And, police say, they were involved in dozens of program abuses and crimes including rape, robbery, heroin trafficking and, in one case, murder.

"It was, in a word, astonishing," said Baltimore City States Attorney William Swisher, who helped spearhead the police investigation that climaxed Thursday with the arrests of 27 of the prisoners on more than five dozen rape, armed robbery, murder and escape charges.

"These were hard-core criminals roaming loose in the streets like animals and nobody was doing anything about it," he said.

For Swisher and other critics of Maryland's troubled prison system, Thursday's crackdown by city police provided fresh evidence that prison officials are too soft on criminals. And the arrests have provoked still another crisis in a state penal system plagued by overcrowding and under pressure from a federal court to upgrade existing prisons and reduce prison populations. f

This latest crisis began Feb. 10 when Baltimore homicide detectives found the body of a 30-year-old man who had been shot in the head. The man was identified as a state prisoner who had been arrested five years ago on robbery charges and sentenced to 18 years in prison.

After interviewing corrections officials, police discovered that the man was a participant in the system's work-release program, and according to records he was enrolled at the University of Baltimore.

Prerelease officials at Jessup, meanwhile, had been alerted to possible inmate abuses of the program as early as December. They conducted their own investigation and after two weeks presented top department officials with evidence confirming their suspicions.

Their report, though, was never acted upon until city police started their own probe. Their investigation into the prisoner's death eventually involved 15 undercover officers and the use of electronic surveillance gear, cameras and a police helicopter. The probe focused on 19 prisoners participating in the prison system's college-release program, and another program in which 11 inmates were assigned to work details in the city penitentiary.

Once they got off the green school bus in downtown Baltimore, police say, the inmates were free to go wherever they wished. According to Swisher, one inmate is the prime suspect in the rape of a 16-year-old girl, while another is suspected of the inmate murder that originally precipitated the probe.

Others have been charged with various holdups of convenience stores, and four men have been charged with drug dealing. Still others were allegedly enrolled in college classes at Morgan State, Coppin State and Balitmore universities that either didn't exist or had been canceled.

Police said one of the men was married while in the program, another secured a driver's license, and one had hired four bodyguards to protect him while he was transacting drug deals.

Ironicaly, the inmates were all serving the last portion of their sentences, which ranged from 10 to 30 years on rape, murder and drug convictions, and the work-release program was intended to help ease their eventual transition to civilian life.

According to sources involved in the investigation, 40-year-old inmate James Cromer, who was arrested for dealing in heroin in 1976 and sentenced to 20 years in jail, led a particularly interesting life outside Jessup.

They said Cromer, who was enrolled at Coppin State College, one day ventured to various stores and specialty shops on Howard Street. He spent time in the morning there at a dry cleaners, a sandwich shop and a liquor store before going to the Trailways bus station, where he made several phone calls.

He then went to Park Avenue and the home of a friend, who investigators suspected was a local heroin dealer. "Every now and then individuals would enter the residence, then exit 30 seconds later," Kane said. "It had all the features of a place from which drugs are dispensed."

Several hours later Cromer hopped into his wife's 1979 white Corvette outfitted with mag wheels, and toured the city, eventually ending up at Coppin State, where he stayed for 45 minutes. After that, Cromer drove the Corvette to the Greenmount prerelease center, where the green bus was due to pick up the inmates at 5:30 p.m. for the return trip to Jessup.

Investigators said Cromer joined other college-release inmates outside the nearby Maryland State Penitentiary, where they were seen passing substances through a chain link fence to penitentiary inmates.

The green bus finally picked the men up and the next morning, at 7 a.m., Cromer got off the bus at Greenmount, got into the Corvette and drove off for another day. "In effect," said one investigator, "some of these guys were like commuters."

It all ended Thursday, though, when police surrounded the green bus near the downtown fish market and the arrests began. Today, at the Brockridge work-release center in Jessup, where the program has been halted pending completion of a state police and grand jury investigation of the prerelease system, minimum security inmates expressed anger that their own privileges, which one inmate called "hard-earned," had been terminated.

Among correctional officers, meanwhile, there was a sense of frustration. "We don't have police powers. Those guys who were arrested were trusties. They were trusted to remain on good behavior," said one guard.

"All we can do is go with the flow. We knew they were no good and were up to no good. But if the system says let them go," he said, "there's nothing we can do about it."