Lack of transparency in city government was Tuesday's theme in the mayoral race, as two possible Democratic challengers to Mayor Michael Bloomberg hammered the issue.

City Comptroller Bill Thompson and Brooklyn-Queens Congressman Anthony Weiner are both going after Bloomberg's record on transparency and accountability.

Thompson is accusing City Hall of withholding documents the comptroller's office is seeking as part of its audit on a program for minority and women-owned businesses. Thompson announced Tuesday that he has subpoenaed a report on the program conducted by an outside consultant.

"Once again, it calls to question, what are they trying to hide in City Hall?" said Thompson. "What are the results in this report that have been found that City Hall is trying to prevent the public from seeing? That is why we issued the subpoenas."

In a speech at the City University of New York Leadership Academy this morning, Weiner argued that the mayor could be doing much more to open up city government.

He challenged the audience to find a copy of the city budget online, and then find out how much money is being spent on transportation, police and education.

"My friends who are here in the media will tell you that it is very easy to go to some City of New York website, but very difficult to drill down into the challenges that we face in any kind of a numerical or prose level in the budget," said Weiner.

A spokesman for mayor disputed the notion that the Bloomberg's administration lacks transparency, and said in a statement, "From top to bottom, beginning with the mayor's own bullpenized City Hall work station, city government has been transformed from an impenetrable entity that frustrated participation into a municipal model of customer service."

In response to Thompson's subpoenas, a spokeswoman for the small business services department said the department intends to give Thompson the documents he wants at some point today and that the department has fully cooperated with the comptroller's office throughout this process.

For more on this story, tune in to "Road To City Hall" at 7 and 10 p.m., where the guests will include another Democratic challenger, Queens Councilman Tony Avella.