"The housing buying power of most Americans is going down-and going down very rapidly," says one of the nation's top urban affairs experts.

And we're not dealing with a temporary aberration but rather a long-term shift," said Dr. George Sternleis, director of the Center of Urban Policy Research at Rutgers University.

Sternleib warned recently at a seminar that exclusionary land-use policies in suburbs are contributing heavily to the rise in housing costs and that if such policies aren't moderated locally, they will be altered by regional or national intervention.

"In 1970, half of the people could afford the median-priced new house," he continued. "By last year, that figure was down to 15 percent. By the end of this year, it may be as low as 12 percent."

He also noted that the average house built last year contained 1,700 square feet with 2 1/2 baths but that it housed only about an average of 2 1/2 people.

He said houses are being bought as a form of savings, not as shelter, and that "the market is being artificially stimulated."

"All economists have underestimated the demand for one-family housing," he said. "We were all using historic relationships to make calculations. The housing market has not turned down. Historically, when prices went up, people waited. Now when prices go up, the consumer says, "I better get on the train or I'll be left at the station.'"

Sternleib said the federal government has insulated housing from the traditional fiscal restraints, but, he added, "We're going back to throwing blocks into housing because we have no options. Housing has led the inflationary parade."

Blaming local land-use policies for much of the inflationary rise in costs, Sternleib pointed out that land traditionally represented 12 percent of the cost of a house but now is 25 percent.

"Speculation has pushed land cost up, and there's a shortage of buildable land. Moreover, the lag time between land acquisition and development has doubled in the last five years," he said.