The city’s highest-ranking fire officer is under subpoena to testify before the City Council today and is expected to attack the Bloomberg administration’s plan for responding to emergencies.

Chief Peter Hayden’s appearance has been the source of disagreement, partly because he called the mayor’s decision to put the Police Department in charge at emergencies that involve hazardous materials a “recipe for disaster,” and partly because, until the Council issued its subpoena late last month, City Hall seemed to be refusing to let him testify.

The fire commissioner, Nicholas Scoppetta; the police commissioner, Raymond Kelly, and the commissioner of the Office of Emergency Management, Joseph Bruno, are also scheduled to appear, but they are expected to defend the administration.

The hearing could revive debate over the city’s long-disputed Citywide Incident Management System, or CIMS, which took two years to draft and was approved by Mr. Bloomberg last month.

After the World Trade Center attack in 2001, the federal government required cities to draft formal procedures for responding to emergencies. Cities that failed to do so were deemed ineligible for “homeland security” funds.

By all accounts, it was a chance for New York to fix some of the problems it faced on September 11, particularly the lack of communication and coordination between the police and fire departments. The chairman of the council’s public safety committee, Peter Vallone Jr., a Democrat of Queens, said more discussion was needed to determine whether the CIMS plan was sound.

During a phone interview yesterday, he said the city’s new emergency plan was an improvement over the procedure in place in 2001, but serious concerns remained. For example, he said that, in some cases, the city does not specify which agency should take charge. That, he said, could “lead to confusion at the top, which will lead to confusion in the trenches.”

Mr. Scoppetta will undoubtedly have to answer questions today about a memo he wrote in February to Mr. Bruno at the Office of Emergency Management, arguing that the Fire Department is better trained for handling hazardous-material emergencies. In that memo, Mr. Scoppetta also pointed out, as the fire unions have done, that the city’s plan would make New York the only city to turn authority over to the police at hazardous-material scenes.

The police commissioner, Mr. Kelly, has argued that New York is unique because it has 36,000 police officers and a well-trained Emergency Response Unit.

Others expected to testify are officials from the fire and police unions and the fire chief of Arlington, Va., Jim Schwarz. That department was the first to respond to the Pentagon after it was attacked on September 11, 2001.

Meanwhile, New York firefighters have a terrorism drill scheduled for this morning while Messrs. Scoppetta and Hayden are testifying.

A spokesman for the mayor declined to comment.