When asked how Christmas sales will fare in the 27 shopping days left before Christmas, Washington retailers invariably gaze heavenward for the answer.

Bright, moderately cold days provide the best climate for the communion of shoppers and the area's merchants. Thus, the area's merchants hope that crisp, clear days will put people in the proper spirit for the holiday retail season, which officially begins today.

"We're looking for a bright, cold sunny Friday," said Leonard Kolodny, manager of the Greater Washington Board of Trade's retail bureau.

Last year, Kolodny recalled, the weather through late December was warm and rainy. Sales were gloomy as well. Outerwear, particularly women's coats, sold poorly in the unseasonable weather.

"Things started to improve after the weather cleared up," Kolodny recalled.

The National Weather Service's latest predictions through mid-December bode well for retailers. Temperatures are expected to range between 34 degrees and 51 degrees, which is normal, and precipitation should be less than the median amount of 2.66 inches for the period between mid-November and mid-December. The weather service, however, doesn't know whether that precipitation will be rain or snow.

But weather is not the only concern facing Washington's nervous retailers. Among their other worries, according to Kolodny, are the state of the economy and interest rates.

"Our credit people have noted publicly that higher interest rates create negative psychological effects on consumers," said a representative for Sears, Roebuck & Co. "We don't know if that will happen this Christmas."

Sears is predicting sales will be moderate -- better than last year -- for the retail industry as a whole, the representative said.

So far, at least, the winners in terms of dollar volume in Sears' holiday catalogue have been washers and dryers followed by electronic games, Star Wars toys, television video games and microwave ovens, the representative said.

Sears, however, has also marked down more items this year than they did last. The company hopes the mark-downs will attract buyers and get its other merchandise moving, she continued.

"People are watching how they're spending their money, so we have to keep our prices as low as we can," she said.

Sears has reported that its profits are off sharply so far this year.

According to Kolodny, Washington-area merchants are optimistic about the season. He said that consumers are beginning to use their charge cards again, following President Carter's March 14 message uring consumers to curtail such use.

"People are just now beginning to have confidence in their plastic again," Kolodny said. "They are beginning to use their credit cards in a more normal fashion. Things are calming down."

However, the Federal Reserve may begin credit tightening again. Interest rates are shooting up once more as the Fed seeks to control the growth of the money supply in an effort to curb inflation.

Woodward & Lothrop, Washington's biggest department store chain and the most common barometer of area retail sales, last year had moderate sales gains during the Christmas season. But profits have been off so far this year.

"We are entering the all-important Christmas season with a well-balanced inventory and in position to take advantage of an improved economic climate, should that occur," the company said in an earnings statement released last week. "If sales do improve in the fourth quarter over present levels, we feel confident that fourth-quarter earnings will match those of the prior years."

But one troubling fact of retail life that may cut into sales in 1980 is simply that there are fewer shopping days between Thanksgiving and Christmas this year than last. In 1979, there were 32 days for shopping; in 1980, there are just 27.