Tom and Jan Powers of Fairfax County are having what they call a "realistic" Christmas. Instead of deparmental-store gifts for the relatives, the Powers, whose air-conditioning business is unusually slow, are giving hand-written, home-composed poems written on old pieces of wood.

But Alex O'reilly of Chevy Chase who recently started making $35,000 a year, is sparing no expense for Christmas. He's spent nearly $300 on gifts, including a single lens reflex camera and an architect's deck. "I think stuff is really expensive, but I'm making enough to afford it," said the programmer analyst.

The Powerses and the O'Reillys illustrate that Christmas 1978 will be one of contrasts in the Washington area. The rich will "have" and the less affluent in the region's broad middle class will "have," too. But perhaps not as much as in Christmas past.

This Christmas is a season underscored by a mood of uneasiness, prompted by fears of inflation, rising prices, and predictions of national recession in 1979. Even Doug Munves, manager of radio and television sales for the trendy Bloomingdale's Tysons Corner store knows he shouldn't be as happy as he is.

His department can't stock enough of the $3,295 Advent 760 Video Beam television sets that project an image on six-foot screens. "It's funny," Munves says, "This talk about a recession. We haven't noticed it here at all. There's no doubt that money is tight and some sales are off."

"Off" is not the word for sales at the China Closet and Martins, a chain of china and crystal stores. "Business is loudy," grouses Ethal Schubert, owner of the stores."We've never had a consistent down period," she says. "Well, since September and October it hasn't been growing."

Other merchants are viewing this year more optimisticaly, but retail sales, most agree, have been "very soft." That's the reason behind what merchants says is an unusually large number of pre-Christmas sales. Designer women's wear is on sale at major department stores, a measure to pull customers into stores.

There are other measures of the Problems merchants are facing in Washington. Nieman Marcus, The Dallas-based high fashion store, has opened its Washington stores on Sundays-something it has never done in Dallas-or elsewhere.

And many are merchants are refusing to talk at all, on indicator that sales are running below expectations. One major Washington retailer canceled an interview, saying the company would just as soon not talk about their sales.

Talking about poor sales, said one clothing store executive "can hurt business."

Some merchants are pointing to Sunday, an "extra" sales day this year, and are saying until they close they will not have a true index of their sales.

In good years the traditional wisdom is taht Christmas sales start early, because people have money and are anxious to spend it. Bad years, merchants say, usually end with a splash.

Sales alone though are not proving a panacea. "Consumers are doing a lot of shopping around, looking before buying and taking advantage of bargains," says William McDonald, vice president of Woodward/Lothrop, one of Washington's major department store chains.

Such caution troubles retail merchants. "Normally at Christmas there is a euphoria, a sort of pay-now-and-suffer-later attitude among people," said a marketing specialist, who asked not to be named. "There is nothing like Christmas for emotional buying."

Not for John Perseo, an employee of the National Bank of Washington, Perseo has approached buying toys for his two sons and daughter with the caution befitting his profession. "We are going for the basic toys this year," he says. "We are not buying each kid a bunch of little things."

One major purchase was a $40 Coleco Telstar Arcade television game. After watching sales, Perseo finally picked up the game at a Dart Drug outlet, but worries that he acted hastily. If he could, he says, he would have waited longer and checked more stores.

Along with the caution in buying Christmas gifts has come an increased reluctance to use credits cards, according to Commercial Credit Co. of Baltimore, a consumer finance company that monitors retails sales in the area. While consumer borrowing remains heavy, the rate of increase in credit card use and consumer loans has declined in recent months, Commercial Credit says.

Ted and Betty Britton of McLean, who together earn nearly $40,000, have tried this month to keep their credit cards in their wallets.

"I'm usually a big user of charge cards," said Betty Britton, an executive secretary for the R. J. Reynolds Tobacco Co. "But I'm a little afraid of what's going to happen next year. I've been trying to pay cash so I don't have a bunch of bills coming in in January."

None of these problems seem to have deterred customers from jamming regional shopping malls-a point that vexes many merchants. "There are a lot of people out shopping." says one sales manager for a chain of television retailers. "They just seem more careful. For the number of people in and out of the store, we feel we should be doing a lot better than we are."

Jeannie Swagger, a secretary at Ocean Data Systems in Rockville, says this year high prices are enough to keep her out of the stores.

"There is this hunting coat that cost $34 last year," she says. "I was looking at it this week and it's now $68. I mean, youknow, that is ridiculous."