The early morning light reveals a no loitering sign and a half-dozen people sleeping beneath it in tents on the Skid Row sidewalk.

A few bony men scatter as a police cruiser rolls up. But Glenda Caldwell isn't stirring from beneath her filthy blankets, sprawled beside a shopping cart filled with crumpled cans and paper.

"Where do you want me to pack up and go? To hell?" Caldwell bellows at the two officers and their sergeant.

Starting this month, a beefed-up police force is arresting people who violate a daytime sidewalk sleeping ban. Plenty worse happens in a neighborhood that for decades has been virtually surrendered to crime, grime and vagrancy but now sits on the fringe of an attempted downtown revival.

Critics deride the sidewalk sleeping ban as overzealous but police Chief William Bratton insists it's a way to salvation for Skid Row. It's the same kind of bust-small-crimes approach he used to control crime in New York City more than a decade ago.

Enforcing the sidewalk-sleeping ordinance is a stark change for a neighborhood where police traditionally have tried to contain crime from spreading, not stop it. The ordinance is considered one of the most restrictive in the nation and has drawn fire from homeless advocates and their allies.

"L.A. remains the only city in the U.S. whose answer to homelessness is to criminalize being poor," said Mark Rosenbaum, a lawyer with the American Civil Liberties Union, which has sued to stop the city from enforcing the ordinance. "A program that relies on criminalization isn't going to solve any of the social problems."

More than 200 of the nation's 250 largest cities have ordinances prohibiting sidewalk sleeping, sitting and loitering, according to a study by the National Coalition for the Homeless. How much these ordinances are enforced can vary day to day, and the group's acting executive director, Michael Stoops, said he'd never heard of another city enforcing a no camping ordinance during the day, but not at night.

The Los Angeles policy highlights intractable issues within the city's largest concentration of addicts, mentally ill and homeless — a population that needs but doesn't always want specialized care.

With 50 new foot patrol officers redeployed to Skid Row, Bratton's Safer City Initiative attempts to improve an area he calls the worst open-air drug market in the country. By enforcing minor crimes, police will erode a long-accepted feeling of lawlessness, he said. Police arrested about 600 people for drug selling in the first week of the initiative.

"We're not here to cure homelessness," said Police Capt. Andrew Smith, who is based in Skid Row. "We're here to ... end what some call a Mardi Gras of crack here, where it's almost a free zone of dope and prostitution and aggravated assaults."

Homeless rights groups and the ACLU, which sued the city in 2003, decry the policy of moving homeless from sidewalks as mean-spirited. A federal appeals court sided with the ACLU in April, classifying enforcement of the ordinance as a violation of the Eighth Amendment that bars cruel and unusual punishment as long as there are not enough beds in homeless shelters.

The issue reached the U.S. Supreme Court. Bratton and others signed off on a proposed agreement that would have allowed overnight sidewalk sleeping but prohibit it during the day and within 10 feet of a business or residential entrance at all times.

The City Council rejected the settlement last month, fearing it was too sweeping and would let the ACLU make similar arguments elsewhere in the city.

Police enforcing the no-sleeping ordinance say there are some 100 beds available in Skid Row on any given night, but addicts prefer to be close to suppliers.

While on dawn patrol of the neighborhood, Sgt. Tim Shaw handed out cards with shelter information to people lying on the sidewalks. Several said they had searched and failed to find space in shelters — or weren't interested for reasons including limited space for belongings.

Counselors who help arrestees clean up and get in a shelter are permanently planted in the booking room. Shaw said a program diverting nonviolent arrestees into treatment for mental illness or addiction is a success, even though only about 14 of every 100 follow through.

"There are women and children there and people trying to straighten their life out," Shaw said. "You're creating a sense of civil obedience and a sense of a safer city."

Some remain skeptical, however, that Skid Row will truly change.

"The effort is really very good, we appreciate that," said Eugene Lorenzana, 59, a Skid Row seafood wholesaler who said he has seen business dwindle because restaurant owners didn't want to come to the neighborhood. "The mayor wants to promote downtown, like in New York, Central Park. But how can you have that with all this?"