Now it's official.

Washington-area residents are more apt to purchase aperitifs and specialty wines, sleeping tablets, Cadillacs, women's fur coats and breath mints than those living in most other parts of the nation.

They also are more likely to weave, collect stamps and go sailing.

But they aren't as prone to buy Tupperware, beer, canned tuna or chewing tobacco as the rest of the country. And the incidence of Washington-area residents doing baking, knitting or making clothes in their spare time is far below the national average.

That is the profile of the Washington-area consumer that emerges from a new marketing study by Mediamark Research Inc. of New York. The study, which was designed to represent a cross section of the population but is skewed somewhat toward middle- and upper-income levels, shows significant variation among major cities in the ways consumers behave and in their buying decisions.

Or at least this variation is shown in the way consumers say they behave, since the study is based on interviews rather than on actual sales figures.

For the study, MRI interviewed 20,000 consumers nationwide during 1981-'82. About half of those interviewed live in 10 major markets--including the metropolitan areas of New York City, Los Angeles, Chicago, Philadelphia, Boston, Detroit, Cleveland, St. Louis and Washington, D.C. About 750 consumers here were interviewed for the study. The other half of the consumers interviewed were scattered throughout the country.

Interviewers collected information on 1,900 product types and 5,700 brands for the study, which is intended to provide data on consumer tastes to advertisers and media.

The study fills more than a dozen volumes. The cost, depending on the size and kind of business buying the information, ranges from a minimum of $2,500 to $200,000 or more. A publication with a smaller circulation generally pays less than one with a larger circulation.

MRI is now in the process of publishing a national version of the study as well as market reports tailored to individual areas.

Meantime, its 1981-'82 study provides details about local consumption patterns that are sometimes predictable, sometimes surprising for an affluent area like Washington.

Take automobiles.

Luxury cars--especially Cadillacs--sell nearly twice as well in the Washington-area market as in the Boston market, according to the study. About 3.1 percent of Americans currently own a luxury car, the study said.

But 5 percent of Washington-area consumers own a luxury car while only 1.7 percent of Boston-area consumers have a luxury car.

Other cities with above-average ownership of luxury cars include Detroit, 4.5 percent; Chicago, 4.4 percent; Los Angeles, 4.3 percent, and New York, 3.8 percent. Cities with below-average ownership of luxury cars include St. Louis, 2.8 percent; Cleveland, 2.7 percent; Philadelphia, 2.3 percent, San Francisco, 2.3 percent, and Boston, 1.7 percent.

A similar pattern was found for Cadillac ownership.

The study said that 1.7 percent of Americans now own Cadillacs. But in the Washington area, 2.9 percent of local residents have Cadillacs. Only 0.9 percent of the Boston-area consumers own Cadillacs.

Then there is alcohol.

Washington, with its penchant for doing business over dinner and drinks, has a higher incidence of consumption of aperitifs and specialty wines than any other major market in the nation. Asked what they had drunk in the last six months, 6.1 percent of Washington-area consumers interviewed said they had had Dubonnet, Campari or some other aperitif or specialty wine. That compared to a national average of 2.3 percent.

To simplify the comparisons of one city to another, MRI devised an index rating, with 100 representing the national consumption average. Any city with below-average consumption scored below 100; any city with above-average consumption scored above 100.

In the aperitif and specialty wine category, Washington had the high of 265 while Cleveland was low with 35. In between were New York, 235; Boston, 196; Los Angeles, 170; Philadelphia, 165; San Francisco, 152; Chicago, 148; St. Louis, 78; Detroit, 70.

The survey found that Washingtonians drink less American beer. The rating for regular domestic beer consumed during the past six months among Washington-area residents was 87--the lowest of any market in the survey. The high was San Francisco's 129. Other above-average beer-drinking cities included Chicago, 114, and Cleveland, 113.

Along with fancy wine, Washingtonians consume large amounts of sleeping tablets, breath mints and men's hair-coloring products.

The sleeping tablet index for Washington consumers, based on use within the past six months, was 122, the highest in the survey. Lowest was Cleveland's 64. Other above-average use was found in Los Angeles, 117; San Francisco, 111, and St. Louis, 106. Below-average cities included Chicago, 69, and Boston, 78.

Washington's breath mint consumption--to cover the wine, perhaps?--was indexed at 113, higher than any other city. The low was New York's 99.

Men's hair-coloring products, purchased for use at home in Washington, had an index of 159, second highest in the survey. Only St. Louis, with 169, was higher. Lowest in incidence of consumption for this category were San Francisco, 67, and Philadelphia, 75.

Women's hair-coloring products, purchased for use at home in Washington, indexed at 100--the same as the national average. But another item usually purchased for and by women--the fur coat--sells at a higher than average rate in the Washington area. The fur-coat index here is 143, not as high as New York's 170 or Chicago's 160 but well ahead of all the other cities, such as Boston's 51 and St. Louis' 79.

Washingtonians apparently spend time and money trying to look good. This may account for the survey's finding of a lower incidence here of activities such as baking, knitting and making clothes at home. The incidence of those three activities was lower among D.C.-area consumers than in any other city in the survey.

Scores included 57 for home-sewing here, compared with the high of 125, which was recorded for both San Francisco and Boston; 36 for knitting in Washington, compared with the high of 254 for Boston, and 68 for baking in Washington, compared with the high of 150 for Boston.

Many of those Washington scores were predictable, given the nature of the city.

But nestled in the investment section of the survey was this surprise: When it comes to securities, money-market funds and mutual funds, Washington, D.C., was the smallest market of the cities surveyed. But when it comes to the purchase of gold, silver and gems, it ranks at the top of the list.