With much fanfare, Mayor Bloomberg spoke on Tuesday about the future of the city. Like many public servants before him, he seeks to leave a physical reminder of his administration, lest future generations forget that he once occupied a wing of City Hall. So he has established a new city agency, the Office of Long Term Planning and Sustainability, to guide the growth he believes the city will experience in the coming decades.

Many years ago, as a college student, I worked as a part-time clerk in the Municipal Reference Library. This allowed me to browse the library’s vast archives, filled with the plans, schemes, and visions of generations of mayors, government agencies, and private do-gooders. I soon learned that little in this collection of good intentions ever came to pass. Some of the plans, viewed in hindsight, were downright comical: 1920s’ visions of a city filled with pedestrian bridges linking the city’s skyscrapers, as dirigibles discharged commuters while tethered to masts at the tops of those buildings.

History tells us that it is impossible to plan on the scale the mayor proposes. As proof, we don’t need to look back all that far. One of the key initiatives of a former mayor, John Lindsay, was the creation of a much-hyped “Plan for New York City,” which was ignored and forgotten.

Lindsay became mayor at a critical point in the city’s history. For the first time in memory, New York appeared to be on the decline. Lindsay surrounded himself with the best and brightest, and was considered a beacon of hope not just in Gotham, but throughout the nation as a visionary of an urban renaissance. He was seriously considered as a potential presidential candidate. Yet Lindsay is remembered not for the grand new city he fashioned, but for the decades of crisis he spurred by nearly spending us into oblivion.

Lindsay was overwhelmed by circumstances beyond prediction, and faced them by making every wrong decision. His signature effort to buy racial peace through a vast expansion of public welfare backfired tragically, both for the city and for the people he thought he was helping. The lesson of the Lindsay years is that any mayor’s hold on the future is doing the best job in the here and now.

Is Mayor Bloomberg repeating history? You can’t project most circumstances a quarter-century ahead. The mayor noted that his office has homed in on the city’s 1,310 playgrounds. Do we need more? Where should they be?

When Lindsay became mayor on January 1, 1966, would anyone have suggested that playgrounds be built among the seedy commercial buildings in SoHo or TriBeCa? Back then, Lindsay may well have sensed a need for playgrounds in Chelsea. But who then could have known that this community would, many years later, become a center of gay life and consequently home to fewer children? It’s tough to predict the future.

Over the next quarter-century, Mr. Bloomberg projects a population expansion that will bring the city’s population to 9 million, up from 8 million. From this he divines a never-ending daily rush hour on the city’s subways, buses, and roadways. But I can make a cogent case that in the future, even with a larger population, fewer people will need to commute to what we used to call the “central business district.” Technology permits me and millions of others to work just about anywhere and deliver reports electronically, even wirelessly. As I write this, am I sitting in the editorial offices of The New York Sun on Chambers Street? Or am I at home working in my underwear? Or maybe, God willing, I am writing this as I sit on a balcony overlooking Lake Como in Italy, sipping an espresso. No one should appreciate this point better than the mayor, who made his fortune delivering information to the financial industry, making it possible to bring Wall Street to your street.

The mayor is on firmer ground when he speaks about our water supply and power needs. This is infrastructure that needs many years to be put in place. Is the mayor ready to tell New Yorkers that more power generation capacity needs to be created — in their backyards? Is he ready to lobby hard to keep the unpopular but critical Indian Point power generation facility open to insure that the region has adequate electrical power? After fighting so hard to insure the quality of the Croton water system, supplying just 10% of our water needs, is he ready to advocate filtration of the Catskill and Delaware water systems providing the lion’s share of the city’s water supply? Which brings us to today. If the mayor is so concerned about growing the city, why has he so consistently backed popular but ill-advised “downzoning” efforts — diminishing the number of units that could be built — in our best residential communities, those where new homes could be built with little public subsidy?

Preparing New York for a larger population means telling those already here that they need to squeeze a bit closer together. That he has added the politically correct term of “sustainability” to his effort, sprinkled his initiatives with references to global warming, and made his presentation at a forum sponsored by environmental activists, is not encouraging. These are the folks who delight, as Senator Moynihan used to point out, in preventing things from being built. If the mayor is serious about leaving a physical legacy, he’d best be prepared to cross swords with, rather than pander to, this crowd.