Senator Schumer and the City Council speaker, Christine Quinn, are among those who do not want to let the biggest real estate sale in the history of New York be left up to market forces.

The lawmakers favor a government-assisted tenant buyout of Stuyvesant Town and Peter Cooper Village that they say would preserve thousands of units of affordable housing for the middle class. The owner of the two giant housing complexes on Manhattan’s East Side, Metropolitan Life Insurance Co., is looking to sell the more than 100 buildings containing about 11,200 apartments for as much as $5 billion.

Some real estate analysts are saying that local politicians are overreacting to a potential sale, and that the government would get more bang for its affordable housing buck elsewhere.

The president of the Real Estate Board of New York, Steven Spinola, said politicians are using scare tactics to drum up publicity.

“Basically, these tenants are protected for life. It doesn’t matter if New York Life owns it, Related Companies, or Vornado. They will have to abide by the law,” Mr. Spinola said.

A professor of urban planning at New York University, Mitchell Moss, questioned whether the apartments’ prices would increase drastically if they hit the open market. He said a sale was not likely to significantly change the neighborhood’s character.

“There has been an enormous reaction to the sale, as if whoever comes in will be able to immediately convert these buildings into the Trump Plaza,” Mr. Moss said. “Peter Cooper Village will never be One Beacon Court.”

Under a new owner, the rent-stabilized apartments would continue on a slow progression toward deregulation, Mr. Moss said.

Currently, about 30% of the units in the complexes are renting at market rates. The remaining rent-regulated apartments are estimated to rent for about half of market rates, giving any landlord a hefty financial incentive to free them up.

A landlord can deregulate a rent-stabilized apartment only if a unit’s rent rose to more than $2,000 and it became vacant, or if the rent is more than $2,000 and its occupants’ income is $175,000 for at least two years in row.

Many argue that the city’s entire stock of rent-stabilized and -controlled apartments will eventually be deregulated through this provision, although it may take decades to do so. Tenant advocates say this process would take between 10 and 15 years for Stuyvesant Town and Peter Cooper Village.

Yesterday, following the lead of the council member who represents the area, Daniel Garodnick, Mr. Schumer and Ms. Quinn said they support the complexes being purchased by an investment group that wants to protect the current rights of tenants, maintain the layout of the property, and give tenants the opportunity to purchase their homes. The group could tap into the purchasing power of union pension funds or banks, the lawmakers said.

“The free market doesn’t always work perfectly, and that’s why government sometimes needs to step in to protect vital institutions and resources,” Mr. Schumer said at a press conference yesterday, where he announced he would seek a federal appropriation.

Ms. Quinn said a sale of the housing complexes would amount to the death of what represented “New York City’s American dream.”

Mayor Bloomberg said yesterday the city “would take a look” at the proposal. The Bloomberg administration has an existing plan to build and preserve 165,000 units of affordable housing, and the preservation of Stuy Town and Peter Cooper Village is not currently part of it.

“Most of the people in Stuyvesant Town or in Peter Cooper Village are protected by the rent stabilization laws. So even if it does change hands, most of them will not find their rents changing other than from whatever the Rent Guidelines Board says,” Mr. Bloomberg said.

Mr. Garodnick said rent-stabilized tenants should be worried that “a new owner may not be so benevolent” as MetLife, and use certain “techniques” to oust them from their homes.

A long-time tenant advocate, Michael McKee, said a sale would not likely directly oust any current rent-stabilized tenants, but that over the next 10 to 15 years the apartments would be no longer be affordable to the middle class.

A 27-year resident of Peter Cooper Village, Shirley Ehrlichman, 78, said yesterday that a sale would be “frightening” and that a new owner could “get around” the rent-stabilization laws to evict tenants.

“Its scary for me. They always say there is a possibility that things are going to change. The state has the power to change the rules,” Ms. Ehrlichman said.