The city Landmarks Preservation Commission yesterday took emergency action to block a landlord from adding a rooftop pad to a 165-year-old building on a classic row-house block off Tompkins Square Park.

Too bad the move came several hours after the city Buildings Department had already approved a permit for the East Village project.

“[The LPC] dropped the ball,’’ lamented Andrew Berman, of the Greenwich Village Society for Historic Preservation.

At issue was a well-kept, $3 million-plus, four-story town home at 315 E. 10th St.

When landlord Ben Shaoul filed for a fifth-floor addition last month, preservationists sought historic status for the block to prevent it.

The LPC had 40 days to act before a permit could be issued. That deadline ended Friday.

The LPC had said yesterday’s hearing date was the earliest it could squeeze into its schedule.