It happens every year, providing evidence about the power of ideas and emotions during the holiday season.

People want to believe--even the normally cynical newspaper and broadcasting reporters who go out to cover the traditional, last-minute Christmas shopping spree or the day-after-Christmas sales. Invariably, when the reporting task is over, the written or broadcast message is the same: A record sales day was had by all and to all a good night.

If you ask a store manager or retail chain president how goes business, 99 out of 100 will be optimistic. On 364 days of the year, this attitude is accepted with a grain of salt because it's part of the trade. Selling goods requires a happy nature, especially in hard times like these when many people are scared and inclined to put any extra money in savings.

But it is Christmas. The store parking lots and cash register lines are overflowing and the natural defenses of a reporter melt away. No one stops to think that a sales record could be just a few dollars more than the previous high, or that a retailer without a sales record every Christmas is a retailer in trouble.

Some time will pass before we really know how good or bad a Christmas selling season Washington business experienced in 1981. The chain stores will report on December volume next month and, to the extent that local business is following the national trend, that will provide one clue.

Later in the year, Woodward & Lothrop will report its fourth-quarter and fiscal year sales and earnings. Woodies is a key barometer because it now is the only locally based major general merchandise retailer, and its year-to-year sales and profit comparisons provide a real measure of local business activity.

Other big retailers, such as the Hecht Co., Garfinckel's, Bloomingdales or Sears, Roebuck, do not provide sales figures on a regional basis.

The final word on Christmas retailing in 1981 won't come until next spring, when the U.S. Commerce Department issues nationwide sales estimates for December that include regional figures. By then, the data will be little more than a footnote to what may seem to be the distant past, as Washington business copes with recession.