After being introduced by his lesbian niece, Mayor Bloomberg made his strongest pitch yet for gay marriage by warning wavering state lawmakers yesterday that history isn’t on their side.

“Do you want to be remembered as a leader on civil rights? Or an obstructionist?” Bloomberg asked in a speech at Cooper Union.

The mayor’s remarks were clearly directed at the Republican-led state Senate, which he has supported with campaign contributions and where the gay-marriage battle may ultimately be decided.

Bloomberg demanded that a vote be taken in the current legislative session because “New Yorkers have a right to know where their elected officials stand.”

Before the mayor took the stage, his gay niece, Rachel Tiven, lauded her uncle as a champion of human rights.

“It’s not hard for him to come to these positions,” she said.