At the Icebox, an alcohol-free, after-hours dance club in Northeast Washington, teenagers 16 and younger are turned away. Several miles away, at a police station lobby in Southeast, an anxious mother waits to pick up her 16-year-old daughter who was out past midnight. And on Good Hope Road SE, two officers pull up to a group of young teenagers, reminding them to head home by 11.

After three weeks--and with differing degrees of enthusiasm among officers--the District's much-trumpeted youth curfew is quietly taking hold, altering the social landscape for some teenagers and hurting some businesses that depend on them. It has been promoted as a tool to fight crime and protect youths from the perils of the night, but officials say it is too soon to measure the curfew's true impact.

Despite the curfew's slow start--only eight youths were picked up in the first five days--interviews with dozens of police officers, teenagers and adults show the new rules are starting to produce results. As of Friday, more than 50 youths 16 years old and younger had been picked up by police and returned home. An unknown number of others were simply told to go home. And in at least one neighborhood, residents have credited the curfew with making their streets quieter.

"I'm happy. I think I've seen officers be pretty reasonable in implementing it," said Terrance W. Gainer, the District's executive assistant police chief. "I think it's much too soon to make a determination about its effect on crime. But it is not only for the kid offenders. To me, it's much more [about] the need to protect kids from being victimized."

On the street, some teenagers think the curfew cramps their nightlife, which can continue well into the wee hours, even on school nights. "You can't have fun," protested Mark Jackson, 15, a Ballou High School student, who likes to attend the after-hours dance clubs.

Late one recent Wednesday, a steady stream of teenagers and young adults huddled under a white canopy to avoid a driving rain outside the Icebox, which opened at 11 p.m.--precisely the start of the weekday curfew. In the past, no identification was required at the club in a warehouse-style building off Bladensburg NE that once housed a meat-packing plant.

But on this night, each patron was asked to produce identification. Those who didn't have any were asked to sign a waiver saying they were at least 17. Those who looked younger, or admitted they were, were turned away.

By 12:30 a.m., club workers said they had turned away at least 20 people who had come to see BackYard, a local go-go band. Some of the youths had to call their parents to pick them up, said Harvey Van Buren, a security worker.

As the night wore on, two girls, 14 and 15, were turned away. They had thought there was no curfew that night because the next day's classes had been canceled by Hurricane Floyd. But Vanessa Williams, 31, came forward, saying she was the girls' relative, and took them inside.

"We're just going to party, that's all," Williams said. "Only reason I'm bringing them, they didn't have to go to school tomorrow."

The promoter, Chris Burch, stood outside near the entrance, lamenting that the curfew has cut business by one-third. At $15 to $20 a head, depending on the night, that adds up. On that night, the club drew about 400 customers.

"We've seen a dramatic loss in our business," Burch said. "We don't have an age limit, but with this happening, we're forced to. It's [even] scared off 17-year-olds."

Other nonalcoholic go-go music clubs, which used to admit all ages, are cracking down as well. On a Friday night, at the Capitol City Pavillion on Georgia Avenue NW, a yellow sign warned: "Curfew Age 17 DOB 9/82". Two off-duty D.C. police officers in uniform stood at the entrance, scanning for curfew breakers. By 1:30 a.m., they had pulled two out of line. One youth looked about 11 years old. He tried to slide inside with his older companions. But when the friends found out the rules, they left him behind. He ran off.

Other businesses are also seeing fewer young customers but haven't been as vigilant about violators. At the Georgetown Cafe, a 24-hour diner on Wisconsin Avenue NW, 15 to 20 teenagers used to drop by after midnight on weekends, said waiter Bassam Dayya. Now, he said, it's more like eight.

"A lot of these young people, you can't tell how old they are," he said. "I can't tell them to leave. It's the law's responsibility."

The curfew has also posed challenges for police. When enforcement began, some officers were unclear about some provisions, or how much of a priority it was. Some police stations lacked the proper detention forms.

Some confusion has cleared, but not all officers are buying into the curfew. Some fear it detracts from more important work. Others complain it's difficult to enforce when so many teenagers don't carry identification. They also cite the law's loopholes. Youths who are running errands for parents or attending school-sponsored events, for example, can go out after hours.

"It's just a matter of having enough officers to do it," said Sgt. Michael Soulsby of the 1st Police District, which includes Capitol Hill and South Capitol Street. "There are a lot more curfew violators than officers."

Sgt. D.C. Groomes, who patrols in Northeast Washington, said police would like a central place to take curfew violators, and for social service agencies to be on call at night if a youth's parents can't be found.

"We need help," she said. "We're not paid to be babysitters."

Some residents of the neighborhoods off of H Street NE, near Union Station, credit the curfew with improving their lives. Six open-air drug markets operate in the area, and some dealers use young children as "mules" to carry goods, police say.

"Before, it used to be like a party going on," said Roland Chavez, 32, who has lived in the area for six years. "Now we can actually sleep."

Chavez expressed frustration with the American Civil Liberties Union, which raised concerns that police would target minorities and low-income neighborhoods. Chavez, who is originally from El Salvador, said his black and Latino neighbors support the curfew.

"Where was the ACLU when I had five people killed on my block?" he asked. "What about our rights? We're living next to open-air drug markets."

On a Friday afternoon in Room 303 of Ballou High School, about 15 students sat at desks arranged in a loose circle. The teacher played devil's advocate, stimulating debate about the curfew. Students read an article on the curfew that she had pulled off the Internet and that was written by a Libertarian group.

"The Constitution clearly states that all people have the right to freely assemble at any time," one student read aloud. "The nine judges on the D.C. Circuit blatantly trumped the Constitution with their ruling."

Few of the students had anything good to say about the curfew. She'maka Barnett, 14, insisted that parents, not the city, should determine curfews. "If your parents let you go [out], you should go," she said.

Mark Jackson, 15, said it's too intrusive. He wants to hang out after hours, as always. "I'm with my boys all night partying at the go-go," he said.

Then he added that he views curfew breaking as a kind of street sport. "We want the police to chase us. That's fun."

On the other side of the Anacostia River, Ben Freed, 15, said he still occasionally catches a late-night music show at an all-ages club such as the Black Cat on 14th Street NW.

"If our parents let us out there, the cops don't have much of a right to tell us where we should be," said Ben, a sophomore at Duke Ellington School of the Arts in Georgetown.

Ricardo Roman, 15, and his girlfriend, Alex Hursch-Cesar, also 15, said they had violated the curfew by going to late movies.

But Gainer said police are most concerned about violators on the streets, at clubs and gathering spots that create neighborhood nuisances. "We're not going in to check theaters," he said.

Most of the curfew violators have been picked up east of Rock Creek Park, where a majority of the clubs are, police say. In the 2nd Police District, which includes Georgetown and much of upper Northwest, police have picked up no violators.

Even on weekends, police in the 2nd District say, there have been few curfew violators. Capt. Marcus Westover said that those younger than 17 often blend in with older friends. "If you came out here and tried to look, it'll be pretty hard to find a juvenile," he said.

Gainer rebuffed any suggestion of selective enforcement.

"I don't think it's a 'north or south of Anacostia' issue," he said, adding that several violators have been picked up in Adams-Morgan in Northwest Washington.

On a recent night, Officer Kenneth Hargrove pulled up to a teenager in the 1900 block of 16th Street SE about 11:30 p.m. When Hargrove asked the youth's age, he quickly confessed: 16.

"I'm coming from my grandmother's house. I was trying to beat the curfew," he said, adding that he was trying to catch a bus to Hyattsville.

Hargrove patted him down, checking for a weapon, then ordered him into the back seat. They headed back to the grandmother's, who confirmed that her grandson had just left the house. "I appreciate it," she told the officer. "Thanks a lot."

Clearly, teenagers aren't the only ones being inconvenienced by the curfew.

One recent weeknight, the mother of a 16-year-old girl who was brought to the police station on Alabama Avenue SE steamed as she waited in the station's lobby at 1 a.m. for her daughter.

"I'm mad at her," said the mother, who gave her name only as Kim. Her daughter, she said, was caught outside after hours with older guys. She had been staying overnight with a friend of the mother's.

Even so, Kim added: "I'm just thankful it's not worse. They could have called me to say she'd been shot in a drive-by."