“I don’t think you can sell fear,” the deputy mayor for economic development, Daniel Doctoroff, says as he sits in the Bronx Conference Room at City Hall, explaining his quandary — he wants New Yorkers to be afraid but would prefer not having to scare them. “You need to sell the need to invest in the future.”

Mayor Bloomberg next month will release a comprehensive plan for the sustainability of the city. It will be based on roughly 18 months of research — overseen by Mr. Doctoroff — into the physical state of the city with an eye toward trying to figure out what things will be like for New Yorkers in 2030. How many people are expected to be living in the city? Working? Visiting? Will New York be capable of handling the changes? Mr. Doctoroff is not optimistic.

“We wanted to know what’s the impact of the city’s growth, could we manage it? And the truth is, we don’t think we can. If we don’t start now, what you’ll see is the city growing, then not being able to meet the demands in terms of quality of life. Cities, like people, like companies, never stay still. Nothing is ever a plateau. You’re generally either going up or you’re going down.

“The fear is that we’re going to see growth that the infrastructure and the environment can’t sustain. Quality of life deteriorating, and then just as happened in the ’70s, you’ll begin to see the decline. That’s what our real concern is.”

Mr. Doctoroff knows very well the lessons of that period — not from personal experience (he’s from Detroit and came to New York because his wife got a job), but from his efforts, ultimately unsuccessful, to bring the 2012 Olympics to New York.

“I became a student of the city and was always surprised by how difficult things were to get done, the lack of big things getting done,” he says of the problem he traces back to the Lindsay administration.

“Lindsay’s big issue was social services versus investment in the physical future of the city. He chose social services, to disastrous financial consequences. You could argue that he was forced into making an impossible choice because of the times, but what happened there does really illustrate the fear that I think should always motivate people in the city: If you do not invest in the physical future, inevitably quality of life declines and it becomes a vicious cycle of quality of life declines, eroding tax base, failure to invest, don’t have the resources, people leave, the tax base erodes further, just spirals down.

“And it can happen very quickly,” he says. “That to me is the most shocking lesson of the late ’60s and early ’70s. When Lindsay was elected, you were starting to see the cracks in the system. By the time he left, and then just two years into Beame’s term, we were teetering on the brink of bankruptcy. Ten years from what people thought was the peak of the city’s power to being nearly bankrupt. So, it does not take time and you cannot take for granted that you will enjoy the good times that you enjoy today.

“That’s our most important message. It would be easy for us to say, ‘We have 1,000 and something days left in office and we’re riding high with the city arguably in the best shape it’s ever been in so let’s just coast.’ That would be easy. But that’s not what we’re all about. The mayor really views his obligation to help prepare the city for the future to be a sacred one.”

That, he says, is where PlaNYC comes in: teams of people taking a top-to-bottom look at the city, trying to figure out what has to be done to keep things on track.

Mr. Doctoroff says they don’t have all the answers, but they have a lot of them.

“It’s a very intensive, analytical look at what the issues are with hopefully real-world solutions,” he says. “That’s what we’re furiously working at now. There will be dozens and dozens of individual proposals, an average of at least 10 different initiatives for each of the goals.”

Some, he says, may “rock the boat a little. You got to be careful. These cracks can become fissures, which can be the dam literally breaking in a remarkably short period of time. There are still a lot of people … with very strong memories of New York’s troubles, when the city was perceived as ‘The Rotten Apple.’

“So there is still that residue of the fear that comes with the memories of those times,” he says. “And that’s not a bad thing.”