The city's Department of Buildings is having a tough time cracking down on illegally subdivided apartments, according to an audit by the City Comptroller's office.

The audit found from July 2010 to June 2011, the DOB's Queens unit was unable to enter properties 80 percent of the time it suspected a problem.

The conversions can be dangerous, sometimes deadly, when fires break out.

Comptroller John Liu, who is expected to run for mayor, took exception with the DOB.

"We were just simply doing a routine follow-up and we were surprised and, quite frankly, disappointed that not only have they not improved, but things have gotten far worse. This is an agency that is so dysfunctional on so many levels. And they need to get up to speed on things," Liu said.

A spokesman for the buildings department says it has aggressively targeted apartments most at risk for fire, including the use of undercover investigations.