425 Park Avenue, before it needed tearing down. (Eral Soto)

In what sounds like a cross between a party and a design crit from architecture college, L&L Holdings held four marathon sessions last week to explore proposals for replacing the tower it owns at 425 Park Avenue with a new modern office building.

Last year, L&L revealed it planned to tear down the 1950s office block and replace it with something new. A complication in the zoning meant L&L had to keep the bottom 25 percent of the building intact, otherwise the developer would be forced to replace the current building with something smaller. It tapped 11 of the world’s top architects to come up with their own plans, then chose four to present preliminary designs, which took place last week.

These starchitects—Rem Koolhaas, Zaha Hadid, Norman Foster and Richard Rogers (all foreigners, including three Brits!)—each gave two hour presentations at L&L’s West 57th Street offices, according to a source, one in the morning, one in the evening, on Tuesday and Wednesday of last week. This was followed by either lunch or dinner at a different nearby restaurant.

An early model of a possible replacement. (L&L)

The architects themselves were on-hand to make the presentation to L&L principals David Levinson and Robert Lapidus and their deputies. There were joined by a design advisory committee led by Columbia real estate dean Vishaan Chakrabarti, CBRE CEO and REBNY chair Mary Ann Tighe, Municipal Art Society president Vin Cipolla and former Landmarks Commission chair and current Hunter College president Jennifer Raab.

According to our source, the designers each presented two different proposals, one in which the 25 percent provision was considered and another where the building could be torn down and replaced at the current floor-area-ratio with no restrictions, at an FAR of 18. There was no discussion of the recently announced Midtown East rezoning, which could allow buildings of exceptional quality to rise to a 24 FAR—50 percent bigger than the current zoning, a bonus that seems to tantalizing to pass up—because the plan had not yet been revealed.

The architects could always come up with such schemes at a later date, as the project is not expected to commence until 2015, when the tenants clear out all at once. Normally, this would present a major challenge for a landlord to re-tenant the building, but L&L has decided to use it to its advantage in replacing the aging structure instead.

Details of the different designs were not available, but they were said to be impressive. "They put a tremendous amount of time and thought into their presentations," the source said. "They were extremely detailed and highly creative in their solutions to the site’s challenges."

The details were confirmed by an L&L representative who declined to comment further. The designs are due to be unveiled sometime in the coming weeks, with a finalist to be announced by the end of the year.

Midtown has rarely factored into discussions of how to reimagine huge swaths of Midtown. That stands to reason: The business district is home to any number of iconic Manhattan buildings, and there is no blot like the West Side rail yards waiting to be transformed.

But that’s no reason to stop reimagining. At least, that’s how the Bloomberg administration sees it. During the mayor’s annual state of the city message earlier this year, Mr. Bloomberg hinted of big, visionary plans for Midtown. And now we’re getting the details. The plan is sweeping, visionary and absolutely optimistic about New York’s place in the life of the nation and, indeed, the world itself.

As The Observer’s Matt Chaban reported last week, the parameters of a truly spectacular reshaping of Midtown has made it to the community board level, the first step in what figures to be a long but hopefully productive discussion of what Midtown east of Park Avenue will look like by the middle of this century.

City Hall plans to redevelop large portions of the Midtown area from 39th Street to 57th Street east of Fifth Avenue, save for a portion of the northern regions of Lexington and Third avenues. Of course, not every building, not every block, will be redeveloped; provisions restrict sites to those that cover an entire avenue blockfront, and the site can be no smaller than 25,000 square feet.

The core of the rezoning plan covers the neighborhood surrounding Grand Central Terminal as well as the Park Avenue corridor between the terminal and 57^th Street. It’s possible, according to city officials, that the Park Avenue of the 21^st century will be lined with towers between 575 and 700 feet, and slightly taller around the terminal.

None of this will happen very soon—in fact, that’s the idea. No new construction under the proposed rezoning could begin until 2017, while the Hudson Yards project on the West Side takes shape. So why push for rezoning now? Why not? The Bloomberg administration has shown a flair for visionary proposals and has the necessarily credibility with the city’s real estate community. Mr. Bloomberg’s time in office is limited, and there is no assurance that his successor will be as committed to recreating and reimagining the city as he and his advisors have.

Ultimately, though, what makes this plan so exciting is its implicit confidence in New York’s ability to pull off such an astonishing makeover of nothing less than the heart of Midtown. This sort of project is not for self-doubters.

It is the sort of grand project that makes New York, New York.

Might Midtown, 1935. (Ephemeral New York)

What perfect timing our good friend Christopher Gray has. No sooner has the city begun debating in earnest the merits of whether or not Midtown East should be upzoned to allow for ever bigger skyscrapers than The Times’ Streetscapist reminds us that such debates, always fervent, are as old as the skyscrapers themselves, stretching back a century and a half.

These were buildings no taller than the Dakota, but in 1885 The New York Times urged restrictive legislation and darkly predicted that “if the streets were lined with eight-story buildings, half of the occupants would be deprived of sunlight, and their children would be etiolated like plants grown in a cellar.” You can tell it’s serious when The Times brings the kids into it.

As tall buildings grew in numbers, architects found themselves in a difficult position. In 1894 the prominent architect George B. Post denounced the skyscraper, as it was now freely called, as an “outrage.” On the other hand the commission he received from his $2 million, 10-story New York World Building, on Park Row — well, that put outrage in a certain perspective.

In 1897 The Record and Guide, alarmed by a proposal for a building 2,000 feet high, protested that New York was open “to attack from the audacious real estate owner” who cared nothing about robbing light from the neighbors, adding, “All that is needed is a barbarian with sufficient money and lunacy.” The Chamber of Commerce, equally alarmed, supported legislation to severely restrict skyscrapers.

The barbarians were by this time usually corporations, often syndicates from St. Louis, Chicago and other cities, where civic conditions in New York did not appear on the balance sheet. What some longhair architectural critic thought was of little moment to them.

No doubt The Times’ editorial board, along with its “longhair architectural critic,” will be weighing in on the latest proposal at some point, with a mix of economic understanding and preservationist alarm. But as Mr. Gray points out “no children had grown into mushrooms” as a result of these 10- and 20-story towers. The same has been the case with those three times as large, so it stands to reason rising to five times the height, 1,200 feet tall or more, should not be The End of Man.

But nor should such benefits be given over to developers for free, or so argues skeptics of the project. It will be the Bloomberg administration’s job to ensure this is a city that will be better off for all, not just some.

Those ants wandering around and through these mighty towers must be considered just as the needs of the hawks perched atop them are.