NEW YORK — Former New York Mayor Ed Koch (D) strongly backed the re-election of Barack Obama in an interview Friday, but worried about the Democrat’s prospects if the president didn’t propose something big.

“Bold,” Koch explained. “That’s what’s required on the part of the president. Because there’s no question, at this moment, if Romney and he are neck and neck, which is what the polls show, the president is in trouble.”

“And I think he’s been a very good president. A very good president,” Koch said. “And I’m for him.”

The outspoken former Mayor and Congressman said he had agreed to campaign for the Obama in Florida, once it got a bit closer to the election.

As for what that bold proposal might be, Koch recommended unilaterally proposing a broad tax reform plan that dramatically cut deductions.

“I am for a flatter tax, which says that everything is taxed. Everything. And you get rid of most, if not all” deductions, he said.

In a wide-ranging conversation, Koch also backed his longtime friend Rep. Charlie Rangel (D), who faces a serious primary challenge in the June 26 election. Koch expounded on his May endorsement of Rangel.

“He’s a man who is always there to help his constituency. He’s been through hell. And I want to see him leave gracefully, feeling good about himself. I suspect this is his last run,” Koch said, noting that Rangel hadn’t told him that directly.

“I believe he made terrible mistakes, terrible mistakes. Bad advice,” Koch said, referring to Rangel’s ethics troubles. “So everybody makes mistakes. And if you take his record of achievement and his war record, they more than pay for the mistakes.”

Koch said he would campaign for Rangel wherever it was most useful to his re-election effort.

Sitting in his 37th floor law office, Koch was in a buoyant mood. He had given a speech to a group of young people earlier in the day on integrity. And Koch chuckled as he recalled the opening line he had come up with for his speech.

“We’re so lucky to live in New York City. It’s such an extraordinary city,” he said. “And because I’m in my 88th year, every morning when I wake up, I look around to see if I’m still in New York City.”