A City Council hearing today on the education department’s capital budget — the pot of city money that goes toward renovating old schools and creating new ones — is likely to become a battlefield for those making the case that poor planning has led to crisis levels of overcrowding and a dire need for new schools.

One new piece of ammunition likely to be discussed: a survey of principals published yesterday that found many dispute official estimates of how crowded their buildings are.

More than half of principals at schools officially listed as “under-utilized” said the listing was incorrect, and 50% of principals said overcrowding sometimes leads to unsafe conditions, according to the report, published by the group Class Size Matters and a local professor, Emily Horowitz, of the sociology and criminal justice department at St. Francis College.

The official estimates are listed in a document known as the “blue book,” which principals quoted in the report said they often dispute. One principal is quoted as saying that the book’s estimates of how many students a building can handle have “no bearing on reality.”

Many principals, nearly 40%, said their schools’ crowding prevents them from offering after-school programs such as sports and tutoring.

The researchers, Ms. Horowitz and the executive director of Class Size Matters, Leonie Haimson, said nearly 500 principals responded to their survey, or about a third of those in the city’s public system.

The Department of Education dismissed the report as unrepresentative because its survey was conducted online and gave no formal definition of “overcrowding.”

“This is more of an op-ed than a survey,” a spokesman, David Cantor, said.

Mr. Cantor said the city is moving to alleviate “pockets of overcrowding across the city” with a capital plan adding more than 38,000 seats over the next 28 months.