The weak housing market, whose severity was underestimated by Federal Reserve officials, will only last about half as long as the eight-year slump that began in the late 1980s, but median home prices in Massachusetts could be pushed downward to a comparable degree, economists say.

And the accelerating foreclosure rate — particularly for those who obtained sub-prime adjustable-rate mortgage loans — is adding to the downward pressure on prices and keeping the market from stabilizing.

While the housing slump of the 1980s and 1990s was fueled in part by an overabundance of inventory and a recession, the economy is expanding moderately today, though economists say the housing market has placed a slight drag on growth.

Alan Clayton-Matthews, an associate professor at the University of Massachusetts at Boston and a director of the New England Economic Partnership, said it took eight years for median housing prices in Massachusetts to return to their previous peak in the last quarter of 1988. During that time, prices dropped 11.2 percent before stabilizing and climbing back to the previous high mark, according to data from the U.S. Department of Housing and Urban Development.

Using data from the Massachusetts Association of Realtors, he said the peak median price of a single-family home at $370,500, in the third quarter of 2005, is not forecast to be reached again until the second quarter of 2009, when it is forecast to reach $372,800, he said.

“That’s a slump of almost four years, so it’s about half the length of the slump of the 1990s,” he said. “What’s difficult to do, and uncertain, is to know how steep the decline will be. What’s a lot more certain is that prices will decline.”

A forecast released earlier this month by the New England Economic Partnership predicted that the median price will drop to $318,000 next year, a drop of almost 14 percent.

Federal Reserve officials acknowledged last week that they underestimated the housing market correction, but said that inflation is the biggest risk to the economy. The housing market in Massachusetts, which saw a more rapid appreciation in prices than nationally earlier this decade, is expected to see a sharper drop in prices and longer duration to the correction.

“The shorter slump reflects that the state is not in a severe recession, as it was then,” Mr. Clayton-Matthews said, referring to the market correction of the ’80s and ’90s. “But the state’s economy is growing too slowly now to support the outrageous prices. Through 2011, we will continue the same steady economic growth we’ve been seeing. There’s no reason to think housing prices can be as out of line with the nation in this decade as the 1990s.”

He said that the housing price-to-income ratio was once the same in Massachusetts as the national average, but that the state’s ratio grew wider than the nation’s in the 1980s. It fell back into line with the national index, but widened again in the late 1990s and into this decade leading up to the current slump.

“The price-to-income ratio used to be the same as the national,” he said. “But now, it’s a lot higher, even given our higher incomes. If our economy were growing as strongly as the ’80s and ’90s, it would be closer.”

In the first quarter of 1980, the median price in Massachusetts was 5.6 times the per capita income, he said. Nationally, it was 6.0, so home prices were actually cheaper in the state in relation to income. But by the third quarter of 1987, in Massachusetts the ratio was 8.3, while in the U.S. it was 5.3.

“So, our prices rose much faster than income and much faster than the U.S. average,” he pointed out.

Then, in the fourth quarter of 1996, after the housing market crash, the state’s ratio had fallen to 5.5, much closer to the national average of 5.0.

“So, it was pretty much back into line,” he said. “It peaked again in the first quarter of 2005 at 8.6 in Massachusetts, and nationally was 6.0. So, it went way out of line again. Now it’s falling.”

As of the last quarter of 2006, the latest for which there is reliable data, it had fallen to 7.6 in the state.

“We’re projecting it to be 6.4 in the second quarter of 2008,” Mr. Clayton-Matthews said. “That’s when we project housing prices will fall to their lowest. Nationally, the index will be 5.4

“We don’t expect housing prices to fall in line with income, but the ratio will be more in line than was at the peak. Even with price declines, we will still have expensive houses here. Even with slow growth, we can still adjust the ratio.”

While median prices continue their slide and the state has about 10 months of inventory available, there are some spots running counter to the trend.

Paul A. Saleba, president of Kettle Brook Lofts LLC, which is renovating the former Duffy Mill on Main Street in Worcester at the Leicester town line, said the slump has not affected sales of the loft-style units in the historic 1870-era brick building. With 52 of the total 109 units being built in the first phase of construction, the developer has seen almost one purchase and sale agreement per day, Mr. Saleba said. The units in the first phase will be ready for occupancy in January or February, he said. The price range is between $139,900 and $300,000 for floor plans that range in size from 515 to 1,700 square feet.

“It’s a combination of factors,” he said of the brisk sales. “We have a rolling brook flowing through and 30 acres of conservation land abutting this. We’ll have walking trails and picnic areas next to the brook. … We’ve been marketing for 35 days, and we have 32 purchase and sale agreements signed. We also have another 10 on deposit.”

And while housing prices continue to ebb, lenders are tightening their criteria for loans after defaults on mortgages rose to record levels over the last year. As the housing market heated up into the earlier part of the decade, more people wanted to get into the market, and sub-prime loans became available to people with bad credit or no credit history, with low rates for the first two years, and increasingly steep rate increases in the following years.

Now, the foreclosure rate, particularly in the sub-prime market, is climbing steeply, and the availability of delinquent properties is adding to the large inventory on the market.

Nicolas P. Retsinas director of the Joint Center for Housing Studies at Harvard University, said foreclosures are prolonging the drop in housing prices.

“The sub-prime problems will delay the housing market recovery,” he said. “It’s one more thing we’re seeing that won’t help the market. Lenders are not landlords, and they’re trying to sell as quickly as they can. That drives down prices.”

Where foreclosures are prevalent, prices will likely fall, he said.

“There is what we call a contagion effect that can be substantial,” he said. “If you look in neighborhoods where there are a higher number of foreclosures, you would see falling values. “Lenders are eager to sell these properties because the longer they hold on to them, the more susceptible the properties are to devaluation.”

He said that as median prices fall and as people tap out the equity in their homes, in the form of home equity lines of credit or home equity loans, they have less equity left in their homes and less money for consumer spending.

“Consumer spending is a good part of the economy, but consumer spending is chugging along pretty well,” he said. “Traditionally, this has had an impact, but this time it seems to be different. There is some lag effect, so it’s difficult to say definitively.”

Mr. Clayton-Matthews said that foreclosures may help the economy in the long run as they make housing more affordable.

“Foreclosures should be bringing prices down in towns where there are a lot of foreclosures,” he said, “primarily those recently financed by sub-prime mortgages. These are primarily middle income who bought recently and didn’t have great credit and needed a sub-prime mortgage to finance the house. It might be that they can’t afford the mortgage when rates adjust upward. Now, with weakness in the market, they haven’t built up equity. I think that’s affecting the middle of the market.”

Worcester was third highest in the number of foreclosure filings between May 1, 2006 and April 30, 2007, according to Foreclosuresmass.com, which tracks foreclosure data across the state. Boston had 2,117 filings, followed by Springfield with 1,270 and Worcester with 1,027.

But one main difference in the economy from the last housing bust was that the national economy is growing, as well as the state’s, though more slowly. Massachusetts’ economy is growing at about 1 percent annually, he said.

Payroll employment growth expanded by an annualized rate 2 percent in 1993, and that continued through the most recent recession in 2001, he said. Now, the state is under 1 percent annual average rate of payroll growth, he said..

Realtor associations have pointed to an increase in sales volumes as a sign the bottom has arrived, but Mr. Clayton-Matthews said volume is only one indicator.

“If you look at year-over-year sales it doesn’t look bad, because you’re comparing the market to when it had already started on its way down,” he said. “Now, it’s at the bottom in rate of sales. The rate of sales should be steady. In a sense, it’s not a bad market.

“In prices, it seems to have improved since last summer, but as we see more defaults, we will see more price weakness. We still have high inventory, and that’s another factor depressing prices.”