Former MTA chairman Joe Lhota announced publicly today that he’s running for mayor.

“I would not have left the MTA, a job and position I loved, if I was not going to run for mayor of New York,” Lhota said in luncheon speech to members of the New York Building Congress.

Lhota would need backing of building honchos in the construction industry to help finance his campaign.

Lhota, a Repubican, served as a deputy mayor under Rudy Giuliani.

Lhota had been telling GOP leaders and associates — in private conservations and meetings — that he was throwing his hat in the ring in the race to succeed Mayor Bloomberg.

But today was the first time he declared his mayoral intentions at a public event, which was held at the Mandarin Oriental hotel in Columbus Circle.