Will this rise be followed by a fall?

What goes up must come down, so the proverb goes. If that’s the case with New York’s real estate market, experts are wondering whether the recent residential sales revival is only a brief pause on a downward slide that pulls the city into line with the rest of the country.

The market is also watching whether the amount of new development coming online will play a part in a decline.

“Right now we’re seeing fairly robust activity, more than we did last year at this time, and that’s contrary to a large portion of real estate markets in the rest of the country,” said Jonathan Miller, president and CEO of Manhattan appraisal firm Miller Samuel.

Barry Hersh, associate director of the Steven L. Newman Real Estate Institute at Baruch College, said the pace inevitably will slow down again.

“New York is the anomaly,” Hersh said. “I just think it won’t continue to soar while the rest of the country is going down. How can New York be an island?”

Some market observers have warned that new condominium development could result in a glut, with an oversupply of units driving prices down. The number of construction permits issued for residential units in the city in 2005 and 2006 was the highest for any two-year period since 1965, and many of those projects are coming to completion now. Despite the slowdown in the market in the past year, only 2.1 percent fewer permits were issued in 2006 than in 2005, according to U.S. Census Bureau figures.

But Frederick Peters, president of Warburg Realty Partnership, doesn’t think there is a problem.

Market saturation is unlikely because fewer new developments are coming online now than near the end of last year, he said.

“It looked more gluttish probably in September and October of ’06 than it does now,” Peters said.

Kathy Braddock, co-founder of real estate consulting firm Braddock + Purcell and the New York real estate company Charles Rutenberg Realty, said, “There are more than enough people out there that are interested in buying.”

Still, by historical levels, condo inventory is high.

Between 2000 and 2006, condo inventory grew by 83 percent, Miller Samuel found. The number of available co-ops rose only a modest 8 percent during that time period.

Last month, there were practically the same number of condos on the market as co-ops, despite the fact that there are three times more existing co-ops in Manhattan than condos.

Looking at both condos and co-ops, overall inventory has been generally shrinking recently, but it is a far cry from the lower availability seen over the last six years.

February 2007 inventory was still higher than February 2001, 2002, 2004 and 2005, and just below the number in February 2003, according to Miller Samuel.

On the other hand, the absorption rate, which is a good barometer of the market, was 7.3 months in the fourth quarter of 2006, according to appraisal firm Mitchell, Maxwell & Jackson, a positive drop from the 10-month rate seen in prior fourth quarters.

“When inventory is above eight months you are in an oversupply situation and prices start to come down,” said Jeffrey Jackson, co-founder of Mitchell, Maxwell & Jackson.

Others remain bullish on the future of the developments soon to hit the market.

Because of the volume of interest, at least two of the 10 new developments Warburg Realty Partnership is marketing — one on the Upper East Side and one in Harlem — are looking to raise prices, Peters said. Granted, the two projects are already almost sold out.

New development — and the prospect of a condo glut — will be hindered, also, because of the changes to the 421-a tax abatement program, to take effect at the end of the year.

“People are clearly taking a second and third look at their decisions to acquire a new site and are recalculating the numbers,” said Steven Spinola, president of the Real Estate Board of New York.

Spinola estimates that that there will be 7 to 12 percent price growth this year.