'Tis the year to be in the Christmas business, associations representing Christmas card makers, Christmas tree growers and Christmas tree light manufacturers agree.

Melanie Howard, public relations manager of the Washington-based National Greeting Card Association, said Christmas card sales are up $100 million from last year. Brisk sales of cards bearing contemporary religious messages and corporate cards sold to women executives have helped push sales from 2.1 billion to 2.2 billion nationwide.

Sales of religious Christmas cards have increased steadily over the past four years, Howard said. The religious message inside is shorter and more upbeat, such as "May the Joy of Christ Be With You During the Holidays," she said. The association attributes higher corporate Christmas card sales to the increase in the number of women executives.

But for the most part, the message in the Christmas card hasn't changed. "Christmas is our most traditional season," Howard said.

Farmers planted the first commercial Christmas trees in 1930 as a way to keep their soil from being blown away. This year, the American public will buy 32 million plantation-grown Christmas trees, according to Jane Svinicki, associate executive director of the National Christmas Tree Growers Association.

"This number of trees sold has been fairly stable over the last couple years," said Svinicki, who noted that buying a Christmas tree is a 400-year-old tradition. Association statistics show that a third of all families in the United States buy real trees, a third buy artificial trees, and a third don't buy a tree at all.

The association represents 2,200 national and 10,000 state members who grow or distribute trees for Christmas.

The NCTGA publishes the "American Christmas Tree Journal," and last year it produced a video tape for junior high school students titled "The Messenger of Life: The Story of the Real Christmas Tree."

Ornament and light sales should be up 20 percent over last season, according to Ron Schoenfeld, president of the National Ornament and Electric Lights Christmas Association (NOEL) . NOEL represents 44 companies in the United States that manufacture and supply everything from Christmas lights to tinsel to the ornamental angels on tree tops.

So far, little clear lights are the hottest new trend in Christmas ornamentation, Schoenfeld said. In fact, these small fixtures are becoming a "tree fashion trend," appearing year-round in malls and for outside decoration in city parks, he said. TRADE

The executive committee of the Washington Board of Trade has selected Peter O'Malley, a Prince George's County lawyer, as its president. O'Malley takes over as head of the organization, which has been described as a "regional chamber of commerce," after two Washington businessmen declined the position in order to devote more time to their companies. Other members elected to the board last Tuesday were: Edmund B. Cronin Jr., chairman of Smithy Braeden Co., as president-elect; Kent T. Cushenberry, director of corporate community relations/government programs for IBM Corp., as secretary; Louise Lynch, president of Courtesy Associates, as assistant secretary; Harry M. Linowes, managing partner of Leopold & Linowes, as treasurer; and William B. Wrench, president of Potomac Mini Storage, as assistant treasurer. The office of vice president will be left vacant until the nominating committe reconvenes in the first quarter of 1986. PROFESSIONAL

The Washington Chapter of the Society of Advancement of Management has elected Glen D. Robinson of The Publishing Group Inc. in Rockville as its president. The group sponsors workshops featuring speakers from major corporations across the country and also holds leadership conferences for professionals as well as students.

The American Society of Training and Development has published a video reference guide for people in the training profession. The two-volume directory describes how to obtain more than 14,000 training videotapes covering management, organization and career development programs. The directory was compiled by the National Information Center for Educational Media.