City officials are downplaying a new list of “persistently dangerous” schools that the state Education Department nearly doubled yesterday, expanding the number to 25 from 14.

Schools with two successive years of serious incidents — such as homicide, sexual offenses, and possession, use, or threatened use of a weapon — make the list. Five city schools fell off the list from last year, while nine stayed on and 16 were added.

The schools stretch across the boroughs. Many are middle schools.

Mayor Bloomberg said yesterday that the expansion obscures an influx of city resources that have improved school safety. “We are working very hard to make sure that all schools are safe,” he said. “Crime in schools is down.” He added, “We certainly aren’t perfect. We will continue to do exactly what we’ve been doing.” A city Department of Education spokeswoman, Dina Paul Parks, said the mayor’s characterization is backed by both state data, which school administrators self-report, and data collected by the New York City Police Department.

“We continue to differ with the state regarding how to distinguish between merely disruptive behavior and behavior with the potential for harm,” she said, pointing out that four of the newly added schools are in the city’s special education district, which caters to children with severe emotional and behavioral problems.

The state’s education commissioner, Richard Mills, said the longer list is a result of more rigorous reporting, not more crime. He said he expects more schools to be added to the list in the coming years as teachers and administrators perfect their reporting strategies.

“I can think of three schools, I believe they were in New York City … where reporting simply wasn’t accurate,” he said. “We reviewed those schools and helped them. Those particular three schools ended up on the list this year.”

The president of the United Federation of Teachers, Randi Weingarten, said reporting is plagued by a “catch-22”: Principals are encouraged to report crimes, but the more crimes they report, the more consequences they could face. “The UFT has encouraged its members to report incidents, but some administrators remain an obstacle to reporting, thus creating an unclear picture,” Ms. Weingarten said.

Ms. Parks said the city will give assistance to schools that have been placed on the list, including more training and assessments, which will begin next month.

The schools, however, will face the possibility of losing some of their pupils. Following a provision of the federal No Child Left Behind law, which requires states build the “persistently dangerous” lists, students at listed schools are given the option to transfer to another school.

In 2006, 624 students requested transfers from schools on the list, and 130 transferred. All of the students were given the option to transfer, Ms. Parks said. Mr. Mills said New York’s reporting requirements are America’s most comprehensive, noting that the state reports more violent schools than any other in the country. New Jersey, he said listed only four last year, as did Texas. California, he said, had zero.