The pending sale of Peter Cooper Village and Stuyvesant Town, the giant World War II-era housing complex on Manhattan’s East Side, could complicate Mayor Bloomberg’s plan to increase the stock of affordable housing in the city.

Housing advocates say the door will open for deregulation if the mega-insurer that owns the 110-building complex, Metropolitan Life, sells it. With billions of dollars on the line, a new owner would undoubtedly be aggressive in trying to make back its investment by accelerating how fast apartments are transformed to market value from rent-controlled, advocates say.

While the East Side housing complex is a private development and does not get city subsidies, many of the units are still part of the city’s threatened affordable housing stock, which the mayor is trying to preserve.

“It flies in the face of the mayor’s goals,” state Senator Liz Krueger said of the pending sale. “You are talking about huge numbers of working people, including many who work for the city, potentially losing their homes.”

Housing experts say, however, that there is no imminent threat because it’s under state law extremely difficult to push out tenants in rent-controlled units. They also note that the city has actually seen a slight gain in the number of rent-stabilized apartments between 2003 and 2005. Many also argue that regulation distorts the market and does little to create affordable housing to benefit those who need it most.

Mr. Bloomberg’s $7.5 billion plan calls for the creation and preservation of 165,000 units of low- and middle-income housing over 10 years, to be completed by 2013. It is the largest plan the city has ever seen.

Some of Mr. Bloomberg’s critics say that while he has taken on affordable housing, his plan focuses largely on creating housing and less on preserving existing housing.

“This sale is the perfect illustration of the hole in the bottom of the bucket of the Bloomberg housing plan,” the treasurer of the Tenants Political Action Committee, Michael McKee, said. “The plan deals only with production. They will never build as much as we’re losing.”

A spokesman for the city’s Department of Housing Preservation and Development, Neill Coleman, said the mayor’s affordable housing plan is the largest of its kind in the nation and is preserving tens of thousands of affordable apartments.

He said “a loss of affordable housing is always a concern” and that the city will work with any potential buyers to ensure that affordability is maintained. He noted that tenants in rent-controlled units would be protected if a new owner purchases the site.

“If a sale goes through, we are not going to see a sudden loss of 8,000 units next year,” he said.

A senior scholar at the Manhattan Institute, Julia Vitullo-Martin, agreed. She said regardless of who owns the complex, rent-controlled apartments will naturally phase out over the next 15 years as existing tenants are replaced. She said the sale “poses no threat to the mayor’s affordable housing plan.”

A spokesman for the state Division of Housing and Community Renewal, Peter Moses, said a sale of Peter Cooper Village and Stuyvesant Town would not dilute any of the protections tenants now have.

“Rent regulations have nothing to do with who owns the buildings,” he said. “People who live in buildings that have rent regulations will continue to live in buildings that have rent regulations.”

Advocates say the case highlights the need for the city to wrest control away from Albany when it comes to decision about rent control.

A spokesman for the mayor, Stuart Loeser, said Mr. Bloomberg supports local control, but doesn’t want “Albany to saddle the City with any additional costs for administering rent control programs.”