To sell or not to sell – that, perpetually, is the question.

The New York Sun surveyed real-estate experts to forecast how much Manhattan apartment prices might increase in 2005, so that the couple cuddling in their one-bedroom apartment in Greenwich Village can finally decide whether to hold or sell.

Those who kept their homes off the market this year have missed out on the 20% price appreciation seen in much of 2004, leaving many to wonder whether 2005 could be a good time to sell.

The report card for next year is mixed.

Some factors that could drag down the market include rising interest rates, a well-performing stock market – meaning investors may take money out of real estate to put it into Wall Street – and concerns that prices of condominium and co-op apartments in Manhattan will flatten after reaching an average of more than $1 million.

Other factors bode well for continued price increase. Mortgage rates have remained stable despite the rise in interest rates; real estate is considered by many experts to be a more reliable investment than stocks, and real-estate values, which withstood the September 11 terrorist attacks, could be expected to weather adverse market conditions.

Real-estate brokerage firms, predictably, have expressed a more optimistic outlook than have forecasters who do not work in the industry. The president of Douglas Elliman, Dorothy “Dottie” Herman, said she is convinced that unless mortgage interest rates rise to more than 8.5%, price appreciation for apartments in Manhattan will range from 5% to 10% next year.

“I would still put money into real estate as long as rates don’t rise too drastically,” she said. “Last year we had 20% to 25% price appreciations, and I say that if rates remain at 8% to 8.5%, then price appreciations will range between 5% and 10%, because there are baby boomers who continue to buy multiple homes, baby boomers’ kids buying homes, and real estate has become such a fashionable investment.”

The chief economist at Terra Holdings, which owns Halstead and Brown Harris Stevens, is Gregory Heym. He, too, predicts price appreciation of between 5% and 10%.The average price of a one-bedroom apartment on the Upper West Side, which was put at roughly $551,000 in the third quarter of 2004, could increase by about $50,000 to $606,000 next year, by his calculations. Those numbers do not take into consideration an apartment’s individual amenities, such as a view of Central Park, an outdated kitchen, or a fickle market, all of which could affect the value.

“Two-thousand-five is not going to see the same increases we saw this year,” Mr. Heym said. “The market cannot sustain that kind of growth, because people will get priced out of the market. Growth of 5% to 10% is more along historic lines.”

The dean of the New York University’s Real Estate Institute, Ken Patton, voiced a less bullish outlook. He forecast that prices will follow the consumer price index, which tracks growth in prices of basic consumer goods. The CPI is roughly 3%, depending on which goods are included.

“I think prices will rise at CPI or a little bit above,” Mr. Patton said. “The larger factor is going to be product, especially because of all the rezonings in the city, the condominium conversions going on, and the many neighborhoods that are being rediscovered and redeveloped.” By adding supply to the market, the theory goes, that growth in “product” could further drive down prices.

Interest rates on 10-year Treasury bonds remain historically low, at 4.14%. Interest rates have not yet affected mortgage rates, which are now at 5.76% and have a longer benchmark, based on a 30-year timeline. Inflation more than interest rates could lead to higher mortgage rates, experts say. So far, both inflation and mortgage rates have remained constant.

“If the 30-year mortgage rates remain under 6%, prices will stay strong, but if mortgage rates rise to a 6.5% level, then it is questionable – I think price pressures could be exerted,” Mr. Heym said.

On the rate outlook, the president of the appraisal firm Miller Samuel, Jonathan Miller, said: “The possible rise of mortgage rates is nothing new, the market has seen this coming for over a year, because as the economy improves it is likely that rates will increase.”

Other factors that could affect prices include the deficit related to war spending and changes in Washington, since the economy is usually less stable in the first year after an election, Mr. Miller said.

Despite the concern about inflation and the deficit, average sales prices in Manhattan were up 16.6% in the third quarter of this year versus the same time in 2003, while price per square foot increased 16.4%, according to Miller Samuel. Median sales prices jumped 13.9%.

“These double-digit increases were all made in a weaker economy than the one we are heading into in 2005, so there is reason to be optimistic,” Mr. Miller said.

An economist at the Federal Reserve Bank of New York, Jason Bram, made a similar point. “If mortgage rates increase because the economy is strengthening,” he said, “I wouldn’t worry too much about the housing market. If the economy is strong, then even if it is more expensive to get a mortgage, people are likely to earn more, so they cancel each other out.”