The city is transforming a 24-acre parcel of land on the Queens waterfront into a village of housing for middle-income families in what is said to be the largest project of its kind since Starrett City was built in 1974 in Brooklyn.

Mayor Bloomberg announced yesterday that the city is purchasing the swath of Long Island City land, which sits across the river from the United Nations, from the Port Authority for $146 million.

The site is the spot on which the city had proposed building an Olympic Village before it lost the bid for the 2012 games.

The mayor called the deal a “landmark moment in affordable housing” and said it would ensure that there is a place for middle-income New Yorkers in the increasingly expensive city housing market.

He said the project would “provide much-needed housing for the real backbones of our city — our teachers, our nurses, our police officers and firefighters, and thousands of other hard-working middle-class New Yorkers.”

The project’s tentative blueprint calls for up to 5,000 units of housing for families earning between $60,000 and $145,000 a year. It is part of the Bloomberg administration’s larger, $7.5 billion plan to create or preserve 165,000 units of so-called affordable housing citywide. The rents are expected to be between $1,200 and $2,500 a month, and the site will also include shops and parks.

The announcement comes two days after Met Life — the owner of Stuyvesant Town and Peter Cooper Village — announced a deal to sell that largely rent-stabilized, World War II-era development for $5.4 billion.

Housing advocates fear the sale of that complex will accelerate the deregulation of thousands of apartments. Some criticized the Bloomberg administration for not stepping in to help fund a tenantbacked bid.

City officials say the Stuyvesant Town apartments are not in jeopardy of being deregulated any faster under the new ownership, and that taxpayer dollars will fetch more by building new affordable housing elsewhere.

The deputy mayor for economic development, Daniel Doctoroff, said the city subsidy on the Queens deal is “roughly half of what it would have cost” to preserve the housing at Stuyvesant Town.

“We can get two units here for every one there, plus we get a major increase in the housing stock,” Mr. Doctoroff said.

In addition to the $146 million the city is paying to purchase the site from the Port Authority — which includes $100 million for the land and $46 million in costs it is assuming — it will also contribute subsidies that amount to about $54,000 a housing unit. If 5,000 units are, indeed, built, that comes to about $270 million, some of which would come from $300 million the mayor recently earmarked for middle-income housing.

Most affordable-housing advocates praised the city for picking a site that sat fallow for years when it was owned by the state.The co-chairman of Housing First!, Roland Lewis, said the project “epitomizes what can be done when state and local government work together and think creatively to build affordable housing,”

He said: “The Queens West agreement should be a model for the use of state owned land to build affordable housing.”

Some said they’d like to see ownership opportunities in Queens. Others questioned the income brackets being targeted.

The director of the Pratt Center for Community Development, Brad Lander, said people earning less than $60,000 should also qualify. He said the median income in Queens is less than $60,000.

The commissioner of city’s Department of Housing Preservation and Development, Shaun Donovan, said the $60,000 to $145,000 range is pegged to the federal median income numbers. The former is roughly 80% of the median income, and the latter is double the median income. “That is the area that we thinking is being squeezed by the success of the city,” he said.

Mr. Bloomberg noted that a two-house income of $145,000 could easily be two city employees supporting a family. City officials say 75% of the overall affordable housing plan is targeted to low-income families. These units are included in the 22,000 the city is building as middle-income housing.

Mr. Bloomberg said the details were still being hammered out as to whether any market-rate units would be included. The city is aiming to issue a request for proposal at the end of next year and to start construction in 2008. The Port Authority authorized the sale yesterday and the city now has 90 days to finalize its plan.