The Redskins are promoting it on the radio. D.C. National Bank is stenciling it on monthly statements. The preacher at Mt. Bethel Baptist Church has talked it up for six consecutive Sundays.

So get ready, Washington. It's census time. Today the large, white envelopes are to arrive in the mail at 86 million homes across the nation. The government wants to know who you are, where you are, whether you are single, married or divorced, whether you finished high school or college, whether your residence has complete plumbing facilities and how much rent you pay.

Behind the promotional fanfare that has accompanied this once-in-a-decade event is the fear that many Americans, even some in this government-saturated town, will refuse to answer.

"I've heard it said that nobody has more distrust of the federal government than a federal employe," said Stanley Matchett of the Census Bureau's field division, only half joking.

Washington, a transient town, took longer to count in 1970 than any other city, he said. A high proportion of single people and two-job families here means that frequently no one is at home when the census-taker comes knocking. Apartment buildings here are often locked. A large number of foreign-born residents have difficulty dealing with the government.

Since federal grants are now tied to population estimates, local governments are making frantic efforts to get every body counted. District Mayor Marion Barry appointed a "Complete Count Committee" of 300 citizens. Last time the census may have missed 3.4 to 5.7 percent of the city's population, according to bureau estimates.

When the 1980 results are tabulated next year, they will show dramatic changes in the metropolitan area. It is estimated that the population has grown to 3,175,000 in 10 years -- an 11 percent increase. The number of households has expanded twice as fast, following a national trend in which people are marrying less and later, and divorcing more often.

As American women have fewer children, the result in this area is a decline in household size from an average of 3.09 persons to 2.76. The change is reflected in the explosion in the number of condominiums and apartments.

The Washington area also reflects another national pattern: the boom of the outer suburbs. Prince William and Loudoun counties and other once-rural areas have experienced phenomenal growth. The 1980 census will tell us who has moved there and how they commute to work -- important in transportation planning.

The broad trends are known because the Census Bureau takes annual surveys.

The decennial headcount, however, provides details down to the last subdivision.

The census is the basis for reapportionment. In Washington it will serve to redraw city council boundaries. In Virginia and Maryland, the boundaries for congressional and state legislative districts will be affected.

It also will resolve a few disputes.

Arlington, Alexandria and other Northern Virginia jurisdictions believe that they have at least 10 percent more people than the state estimates, and that they are being shortchanged in federal dollars as a result.

For months, the 25 members of Arlington's Complete Count Committee, headed by Washington attorney John Milliken, have been making speeches and handing out leaflets on the census.

"We have 50 language groups for whom an English-language questionnaire designed for a computer is not only unreadable but outside their cultural experience," Milliken said. "A lot of them come from places where government is something to be avoided."

Thus the Arlington group has put up posters in Vietnamese groceries, set up a volunteer office in the Korean youth center, assembled Spanish-speaking aides and even tried to persuade Iranian students to cooperate in the effort.

In a two-story, green frame house in Anacostia, Mary Brisker, 42, a community worker, has been trying to carry the census message to the city's less affluent communities. She has met with tenants at Arthur Capper public housing, judged census poster contests at Ballou and other high schools, and given some 200 speeches to church and social groups.

"Our biggest problem is persuading people that their answers will be confidential," she said. "We have a lot of people living in public housing getting (welfare) checks. They have living arrangements with their mates. They think the government will find out and cut off their checks."

Most people will be asked 19 questions. One out of five randomly picked Americans will get a 65-question form. The questionnaires are to be mailed back postage-free to the Census Bureau by Tuesday.

In mid-April, census workers -- some 4,000 in the Washington area -- will begin calling and visiting those who have not returned forms. Those who refuse to answer can be fined $100.

Census Bureau expects about 80 percent of the population to return the form by mail. On April 4 and 5, some 80 census-takers will fan out across the District to count people in missions, flophouses and all-night movies.With the help of Mitch Snyder, they will even seek out those who sleep in abandoned alleys and on hot-air vents.

Illegal aliens who have flocked to the area in recent years are another hard-to-count group. "I'm sure they won't answer," said Estelle Berdeguez, a census worker in Adams-Morgan. "They're going to pitch the form. The Hispanic community in general is very suspicious."

Mayor Barry, however, says "I'm optimistic. I didn't see nearly as much activity in 1970. We'll have more people counted this time." Barry has agreed to attend a Census Disco to raise money for census activities. First prize is a dance with the mayor.