The financial fallout from defaults on subprime mortgages is threatening housing markets everywhere, but at least one area of New York City’s real estate market, residential rental apartments, appears to be thriving.

“The reality is there’s no real evidence the subprime situation has influenced the city’s rental market in any way, shape, or form,” the chief operating officer of Citi Habitats, Gary Malin, said.

In July, the average rent of a one-bedroom in Manhattan was $2,609 and a two-bedroom was $3,845. The vacancy rate was 0.81%, according to data from Citi Habitats, one of the city’s largest rental brokerages.

“There’s very little direct link between subprime and New York’s residential rental market,” a real estate economist at independent real estate research and advisory firm Property and Portfolio Research, Andy Joynt, said. As of the second quarter, the average monthly price for a rental apartment in Manhattan surged 8.8% over last year, to $3,694, according to the firm. It predicts that rents will rise another 20% to reach $4,362 by 2011.

The current credit crunch may actually boost demand for rental apartments, as fewer potential home buyers will be able to finance a mortgage, the executive vice president of Glenwood Management, Gary Jacob, said. “To the extent people are having trouble getting the favorable terms they want on mortgage loans, that would certainly drive them to rent,” he said.

But the impact of higher mortgage rates and additional demand for rentals will likely only have a marginal effect, experts say.

“There’s so much demand for these apartments already,” Mr. Malin said. “I doubt that individual landlords will recognize a few more people entering the market and increase prices even higher than they already planned to.”

More important may be that a severe downturn in the economy could lessen demand for rentals. “I think the main threat from the subprime crisis is the possibility that it spreads and creates a bigger, widespread financial crisis on Wall Street,” a senior vice president of development for Avalon Bay Communities, Fred Harris, said. Plummeting financial markets would lead to a drop both in apartment sales and rentals, each of which is driven in part by the employment and bonuses of Wall Street employees, and by New Yorkers invested in the markets, he said.

The rental market could be affected if more developers convert their condominiums into rentals — a reversal of a years-long trend. According to Mr. Joynt, there is a less than 30% chance for an economic depression severe enough to create this scenario. And even then, the combination of New York’s limited space for new construction and its complex regulatory environment makes it difficult to build enough new apartments to keep pace with the city’s perpetually high number of renters.

“In New York, you didn’t have the pure speculation that you had in other areas of the country over the last several years,” the director of acquisition and development for Toll Brothers, David Von Spreckelsen, said. “Here we’ve been building more fundamentally into existing, pent up demand.”

That the rental market will likely continue to be strong bodes well for landlords and brokerages. But it may be lamentable for certain groups of renters: “It’s nothing new that the New York rental market is tight. But for those looking for an apartment in Manhattan who have to cram six people into a two-bedroom apartment, it’s a tough situation,” Mr. Joynt said. “For them, frankly, a decline in the rental market would be no bad thing.”