D.C. police Officer Albert Parker had never seen so much crack in one place on the street before. "Look!" he yelled to his partners in a hidden observation post in the 200 block of V Street NW. "This man's got all the dope in the world!"

The police found 80 plastic bags of crack when they caught up with Anteous Winslow a few blocks away. What they didn't find was the supposedly nonremovable radio transmitter he was ordered to wear while awaiting trial on a murder charge, part of an electronically monitored house arrest program. The ankle bracelet was back at his house, still signaling a D.C. Department of Corrections computer that all was well.

Winslow is in federal prison now, serving a five-year sentence for cocaine distribution, and his arrest in April prompted corrections officials to buy new "tamper-resistant" ankle bracelets. But the ease with which he slipped out of the bracelet and through a state-of-the-art electronic net illustrates a growing national problem.

As the number of drug offenders has surged, so has the demand for prison alternatives -- including monitoring programs in which offenders are allowed back into the community wearing radio transmitters.

Attached to the wrist or ankle, the bracelets signal probation officers whenever the wearer violates curfew or, in the case of someone under house arrest, leaves the premises.

But the system has proved far from foolproof. Some offenders have found ingenious ways of circumventing even the most sophisticated monitors, and the transmitters don't stop anyone from selling or using drugs at home or engaging in drug crimes during non-curfew hours.

The dawning realization that electronic monitoring is no panacea comes at a time when its use is increasing. Joseph Vaughn, editor of the Journal of Offender Monitoring, estimates that there are about 12,000 people under electronic monitoring today; the number is expected to reach 70,000 in a decade.

The biggest company in the field, BI Inc. of Boulder, Colo., pioneered the use of the devices on cattle in the late 1970s and moved "from cows to cons" in 1983, a spokesman said. Today, BI does business with prison systems in 33 states.

In Maryland, electronic monitoring is used in at least six jurisdictions. Among them is Prince George's County, where a judge approved bond for Jerry Samuel Tyler, charged in last week's killing of James S. "Jay" Bias, with the provision that he remain under monitoring in his parents' house.

In Virginia, nine jurisdictions use the devices. Dan Catley, a spokesman for the Virginia Department of Criminal Justice Services, said the programs are popular with the state legislature because they offer cheap alternatives to prisons.

But many sentencing experts fear that the rush to electronic monitoring will doom it to failure. Not only do the bracelets fail to deter drug crime, they say, but the large number of offenders using them increases the chance that a violent crime will be committed by someone who slipped through the net.

Such developments can turn public opinion against such programs. "If you want to let your program get shot down, let it get a lot of attention in the media," said Nic Howell, a spokesman for the Illinois Department of Corrections.

Howell should know; he's been fielding inquiries about his state's program since Nov. 28, when an 18-year-old car thief -- one of 460 offenders electronically monitored in Illinois -- lured a man to his Chicago apartment with the promise of a drug deal, then robbed and killed him.

"The machine worked fine," Howell said. "He was not outside his {radio} range when he did his crimes."

Similar stories can be found in the District, where the pressure to put offenders under monitoring is especially intense because of the city's severe prison crowding and high rate of drug crime. Sixty-six percent of those on the four electronic monitoring programs run by the District are drug offenders, three times the national average.

Not surprisingly, most of those who have slipped through the net here are drug offenders. The 5th District officer who arrested Anteous Winslow testified that it was the third time he had caught someone selling drugs who was supposed to be at home wearing a bracelet.

The monitoring systems are designed to prevent that from happening.

At their heart is a central computer that makes random telephone calls to the offender's house. When the call comes, the wearer of the bracelet has to insert it into a black box, completing an "electronic handshake" to let the computer know he is there. The system is backed up by a radio receiver that emits an alarm if the wearer leaves its range during curfew.

If the offender is allowed outside -- to hold a job, for example -- the receiver lets the computer know when the person leaves and returns. If anything goes wrong, the computer immediately calls the person's probation officer.

But the system can be fooled.

In a case last October before U.S. District Judge Gerhard A. Gesell, Lizette Calderon, accused of carrying more than five kilograms of cocaine from Miami to Washington, failed to show up for her trial.

Two U.S. marshals were sent to find Calderon, but instead they found her electronic bracelet -- neatly cut in half -- in an Arlington town house two blocks from where she was supposed to be living.

Denise Shelton, the Corrections Department official in charge of the District's electronic monitoring programs, said last week that it was unclear when Calderon left town. The last successful computer check on her was at 4:04 a.m. on the day of her trial date, Shelton said; when Calderon's counselor got a signal at 7 a.m. that something was amiss, she assumed Calderon had left to go to court.

Calderon's tamper-resistant bracelet was supposed to signal the computer if anything broke the circuitry in the band, Shelton said. But that works only if the band is cut while the wearer is within the 200-foot range of the radio receiver attached to the home telephone.

There are other glitches. It's possible, though not easy, to slide the bracelets off without undoing them. Shelton said that if that is judged to be a risk with a particular offender, the bracelet is placed around an ankle, where it's harder to remove.

Then there is the question of radio range. On a street of narrow row houses, the 200-foot range of the radio receiver could encompass several addresses. The offender could be several doors away and still not trigger the alarm.

"Technology will not stop someone from either absconding or doing something they should not be doing," said Richard Angulo, director of sales and marketing for Hitek Inc., a Florida company that sells the transmitters and computer software used by the District. But he said his firm's statistics show that only a small percentage of the people on electronic monitoring try to tamper with the bracelets.

Still, some of the problems have caused some judges here to swear off electronic monitoring altogether. In the Calderon case, an irate Gesell told a supervisor from the District that his program was finished "as far as this courthouse is concerned." Privately, other federal judges have said the same.

That is what sentencing experts such as Mark Corrigan, who teaches at Brandeis University, say they fear. Used as a way to put nonviolent and some first offenders back into the community while making restitution, electronic monitoring can offer huge savings, he said.

"But if we don't do it carefully, we're going to lose it as an option," he said. "When we put the wrong people on it and they go out and screw up, it's not because the bracelets didn't work. It's because we use it for the wrong people."