If anybody tells you that new federal statistics demonstrate that home real estate values are falling in many U.S. markets, call economist Marshall Kaplan of the Federal Home Loan Bank Board.

He'll tell you that that's preposterous, ridiculous, bizarre and just plain wrong. Kaplan was astonished to learn in a recent Wall Street Journal article that his agency's monthly housing sales price data now show that "the average sales prices of homes in 32 metropolitan areas declined percent, or $17,056 from the peak average of $94,534."

The article cited analyses of bank board data made by John Wesley English, a Walnut Creek, Calif., investment adviser who writes and speaks widely on "the real-estate crash." Two years ago English predicted a 50 percent decline in the average value of home real estate by 1984.

Through his nationally circulated, monthly investment advisory newsletter, English argues that the crash is well under way, and that prudent homeowners should give serious thought to selling now before the real-estate economy deteriorates even further.

He offers city-by-city price trend summaries and impressive graphs to prove how fast housing prices are heading downward from their "peaks" during the prior 18 months.

The problem with English's conclusions -- and those of other economic doomsayers who are dominating the nonfiction best-seller lists -- is that they're based on controlled uses of real estate data.

For example, English relies heavily on the monthly average sales-price data for 32 metropolitan areas compiled by the Federal Home Loan Bank Board from local mortgage lenders. He points out that Atlanta prices are down an average $6,000 from where they peaked prior to the onset of the 1980 money crunch; Baltimore prices are down by $8,800; Chicago by $14,000, Denver by $20,000, Philadelphia by $16,000, Kansas City by $18,000 and Washington by $21,500. San Francisco prices are off $16,000 from their peak in April 1980, Los Angeles is down by $23,500, and Seattle prices are down by nearly $27,000. Poor Milwaukee's December 1980 price level is off $42,100 from its average $113,800 of July 1980.

All of these decreases are taken straight from Federal Home Loan Bank Board's statistical studies, says English. And he's absolutely right. b

What he neglects to mention, though, is that the Federal Home Loan Bank Board itself warns against reliance on its month-to-month samplings of prices because they're highly prone to volatile up-and-down swings, seasonal variations, and often represent only a tiny fragment of the transactions under way in any given market.

As Kaplan puts it, "We would never take an unusually high monthly salesprice average from a market -- a sudden blip up to $125,000, say, in a market whose prices tend to be in the $80,000-$90,000's -- and then define it as some sort of 'peak'. That's ridiculous.

"Nor would we accept an unusually low monthly sampling figure for a market -- like $75,000 in a city with a normal average over $90,000 -- as some sort of indication that prices were dropping through the floor. We look at price movements over time -- over an entire year -- in order to get a true sense of what's happening in a market."

And the fact is, adds Kaplan, that on a yearly average basis, every major market in the United States shows increases in housing prices during 1980 over 1979 -- often in the double digits. Nationally, the average sale price in the Bank Board's surveys went from $69,500 in 1979 to $78,800 in 1980, a 13 percent jump in 12 months.

There are no markets where long-term prices are headed downward, even those in the most economically distressed parts of the United States, like Detroit, Newark, Rochester and other northern industrial cities.

The Federal Home Loan Bank Board doesn't rely exclusively on its own annual data to draw conclusions either. Kaplan says the government believes the detailed statistics on home resale prices collected by the National Association of Realtors from 142 local realty boards provide "the most accurate and broadest feel for what's really going on out there" in terms of values and prices.

The December 1980 reports from these boards showed the median price nationally through November to have been $64,300 -- up 15.6 percent from the $55,600 median the year before. The northeast region of the country racked up the biggest median price increase -- 23 percent (from $51,700 to $63,600). The western states' median rose to $90,500 from $80,300 the year before (up 12.7 percent). Southern markets jumped to a median of $60,700 (up 16.3 percent) and the north-central states' median rose by 12.8 percent (to $53,600).

There's no need to belabor the point: Ask the gatherers of federal statistics about prices and values in U.S. markets before you run out and sell your house in a panic.

In Kaplan's words: "There's apparently a huge group of people out there who are perfectly willing to believe that everything's headed to hell in a handbasket -- specially real estate. And there's a growing group of 'investment advisers' who appear to be perfectly willing to tell them exactly what they want to hear."