The leading Democratic candidate for mayor, Fernando Ferrer, pledged yesterday that if he is elected he will boost property taxes by nearly $1 billion in the next decade to help build and preserve 167,000 units of “affordable housing.”

The announcement marked the third major policy pronouncement of the Ferrer campaign, and the second time Mr. Bloomberg’s top challenger has proposed a major tax hike. Mr. Ferrer’s first taxation priority, announced in April, was a “stock transfer tax” that would levy $1 billion a year on stock transactions to pay for what he considers to be the city’s share of the bill in the Campaign for Fiscal Equity school finance lawsuit.

The newest taxation scheme, announced yesterday morning outside an affordable-housing complex in the Bronx, would raise almost $1 billion over 10 years as part of a complex, $8.5 billion program. Mr. Ferrer’s plan is significantly more expensive than Mayor Bloomberg’s affordable-housing plan, announced in 2002, which is expected to cost $3 billion over five years, but the former Bronx borough president said it was crucial because the city is facing “one of the worst housing crises” it has endured, a situation that is “crippling” hundreds of thousands of middle-class New Yorkers.

“Everyone in this city knows we are in a real housing crisis,” Mr. Ferrer said. “Well, everyone except Mike Bloomberg.” With that, and a bit of reminiscence about his childhood on Fox Street, when Con Ed constantly threatened to turn off his family’s gas, Mr. Ferrer launched into a lengthy explanation of his proposal. Probably the most controversial part of the plan is for the city to raise almost $1 billion in revenue over 10 years with a new “anti-speculation assessment.” Mr. Ferrer said that under the proposal, vacant residential properties would be taxed at commercial property rates, instead of residential property rates.

He said the proposal was intended to encourage landowners to develop affordable housing on vacant lots, but the Bloomberg campaign said yesterday the plan – which would require a change in state law – would make it harder for landowners to build new homes and boost the prices of any new houses that are eventually erected.

Another piece of the Ferrer plan would require all developers seeking the property tax exemption known as “421-a” to devote 20% of their development projects to affordable housing. That means they would charge below market rates for at least a fifth of the units – even if they’re built in struggling areas such as the South Bronx, where market rates are relatively low.

“These changes will transform these programs from an unwarranted sop to developers into a meaningful tool for promoting affordable housing for average New Yorkers that could create or retain up to 10,000 units of affordable housing over 10 years,” Mr. Ferrer said.

The Bloomberg administration already requires developers to include submarket-rate housing in projects in areas of the city that are thriving, if they want to receive the tax break. Bloomberg administration officials said making the tax break harder to get in areas such as the South Bronx would remove an incentive to build new housing and decelerate development that has been made possible, in part, by the incentive.

The tax components account for only a fraction of the $8.5 billion program. Mr. Ferrer would finance the bulk of the plan by reallocating existing city and federal revenues. Almost $4.5 billion would come from the city’s capital budget. Another $1.1 billion would come from the federal government. Mr. Ferrer’s aides said he has no plans for how to plug the hole that would be left in the city budget if the federal Community Development Block Grant money is transferred to an affordable-housing fund from its current use, paying for housing maintenance code enforcement.

Mr. Ferrer also proposed taking $800 million in Battery Park City revenue from the city’s general fund and directing it to affordable housing. Again, campaign aides said there was no plan for filling the hole left by the real location of resources.

Yesterday afternoon, as word of Mr. Ferrer’s plan filtered around the city, authorities on affordable housing said that the plan sounded promising – but that it was too soon to know. The senior housing policy analyst at Good Jobs New York, Victor Bach, said: “Any plan that makes an $8.5 billion commitment over 10 years, that commits $800 million of Battery Park City funds to affordable housing … deserves attention.”

The Bloomberg campaign, though, didn’t reserve judgment. “Freddy funds his plan through a nearly $1 billion property-tax hike,” a Bloomberg campaign spokesman, Stuart Loeser, said. “Coupled with his stock-transfer tax to fix the schools, it seems there is no problem that higher taxes can’t solve.”

A spokeswoman for the Ferrer campaign, Jen Bluestein, shot back: “Under Freddy’s plan, no home or business will be subject to a tax increase.” In a statement, she added: “There’s only one candidate in this race who has a record of raising taxes – Mike Bloomberg.”

Mr. Loeser also accused Mr. Ferrer of mixing up his facts or lying when it came to describing what the mayor has accomplished on the affordable-housing front. Mr. Ferrer said repeatedly in his speech that Mr. Bloomberg has built only 10,330 units of affordable housing, out of 68,000 he promised.

Ms. Bluestein said it seems Mr. Bloomberg has his own numbers wrong. “According to the glossy, eight-page mail piece Bloomberg sent out last week, he’s only produced 24,656 units,” she said. “Bloomberg’s housing plan is nowhere near target.”