After a second loss in federal court for the city, the Bloomberg administration is barred from enforcing a recent anti-graffiti ordinance.

Sections of the ordinance, which the City Council unanimously passed last year, prohibit 18-, 19-, and 20 -year-olds from purchasing or carrying cans of spray paint or broadtipped markers on city property. Several art students filed a lawsuit challenging the law in April, claiming that it interfered with their work and that they risked arrest every time they carried their art supplies to class.

Lawyers for the city have shown little sympathy for the claims of these students and asked the court to allow the police department to continue enforcing the ordinance as the lawsuit was litigated. But in an order released Wednesday, a three-judge panel of the 2nd U.S. Circuit Court of Appeals ruled that a lower court’s order against the city should go into effect immediately.

The judges on the panel were John Walker, Sonia Sotomayor, and Jon Newman.

A lawyer for the art students, Daniel Perez, interpreted the order as a significant sign that the federal courts were skeptical of the law and would likely rule against it.

“This law has been on life support for the last month,” he said. “The 2nd Circuit just pulled the plug.”

But one expert on the First Amendment said that it would be a mistake to examine the order for a clue of how the court might ultimately rule on the issue.

A University of Chicago law professor, Geoffrey Stone, said that the ruling demonstrated only that the court found the city would not be harmed if it ceased enforcing the ordinance pending the outcome of the lawsuit.

“It is certainly not a guarantee that the plaintiffs will win the case,” he said.

Mayor Bloomberg has followed the lead of his predecessor in making anti-graffiti efforts a core part of his “quality of life” campaign. The police department has a unit devoted specifically to fighting vandalism and offers rewards for information that lead to graffiti convictions, according to data from the mayor’s office.

The commissioner of the Mayor’s Community Assistance Unit, Jonathan Greenspun, reports that his unit has removed more than 70 million square feet of graffiti since 2002. He sends out as many as 20 work crews each day to clean graffiti, he said.

“We are disappointed that we will not temporarily be able to enforce the stronger provisions of the anti-graffiti law,” the lawyer arguing the case for the city, Virginia Waters, said in a statement yesterday. “Graffiti is an ongoing blight in New York City, and we look forward to being able to use this important tool once we prevail upon the appeal.”

To date, the police department has rarely enforced the sections of the ordinance in question. Ms. Waters told the court that the officers have used the law to issue only two summonses to 18-, 19-, and 20-year-olds for carrying “graffiti instruments.” In comparison, the police department has invoked the state’s basic anti-vandalism law in more than 870 arrests this year.

The appellate court wrote, in its paragraph-long order, that the art students “face irreparable harm based on the alleged violation of their constitutional rights.”

Under the ruling, the police department can still enforce the provisions of the ordinance that prohibit minors from carrying or purchasing spray paint or broad-tipped markers.

The lawsuit is currently before Judge George Daniels of U.S. District Court in Manhattan. In early May, Judge Daniels had ordered the city to cease enforcing certain provisions of the ordinance. His order had been stayed until Wednesday’s ruling.