The Independent Budget Office said yesterday that even if the real estate market cools and interest rates rise, the city can expect revenues from property transfer taxes to be consistently higher than they were in the past.

The IBO report comes about two weeks after the Bloomberg administration announced that the city’s projected deficit for next year was down to $2.3 billion from $4.5 billion because of healthier than expected revenue forecasts driven mostly by the strong real estate market.

At the time, however, city officials said the revenue increases were “unlikely” to continue because they were being generated by “our most volatile tax revenues.” But the IBO, an independent city agency that acts as a budgetary watchdog, was more optimistic.

Much of that optimism was attributed to the significant spike in the number of homes being purchased for at least $500,000 – the threshold that triggers an increase in the tax on mortgages and purchases to 1.125% from 1%.

An economist at IBO, George Sweeting, said barring a collapse of the real estate market the city could count on higher real estate transaction revenues than it had a few years back.

Mr. Sweeting said there appeared to be a “permanent upward shift” that would ensure that even if prices dropped slightly, there would still be more homes selling for at least $500,000 than a few years ago.

“At least some of the recent tax revenue growth is probably locked in thanks to this bracket creep,” Mr. Sweeting wrote in the report.

A breakdown in the report shows that there were about 70,100 homes sold in the city for under $500,000 in fiscal year 2000 and about 13,800 sold for more than that amount. Those fig ures are far different that the roughly 66,000 that sold for under $500,000 in fiscal year 2005 and about 33,000 that sold for more.

A senior fellow at the Manhattan Institute, Nicole Gelinas, said it was logical to wonder whether the city should increase the $500,000 threshold or implement a flat real estate transaction tax rate.

“I would imagine that when they enacted this tax, $500,000 was a lot of money to pay for a house and now it’s really not,” Ms. Gelinas said. “That’s a house that will land you straight in the middle class in New York.”

A spokesman for Mayor Bloomberg, Jordan Barowitz, said the city’s Office of Management and Budget was aware of the $500,000 threshold, but that it had a “more cautious” view of the real estate market and viewed its figures as more accurate. Mr. Barowitz said, “We’re not as optimistic.”

The IBO report found that collections from the mortgage recording tax and the real property transfer tax – the two taxes in question – exceeded $1 billion in 2005. That was up from $500 million in 2003 and up from between $100 million and $200 million in the mid-1990s.