Thousands of Christian booksellers are gathered in the lion-size Washington Convention Center for the 34th annual Christian Booksellers Association (CBA) International Convention where they are ordering nearly one-fifth of total yearly sales of books aimed at evangelical Christians.

CBA officials say the boom in evangelical publishing has slowed, but business remains brisk. Videotapes, books dealing with family issues and theological reference works have become the newest hot-sellers in their $1 billion a year industry, they said.

Conventional publishers and record companies, however, are beginning to pull out of marketing efforts aimed at the specialized religious marketplace, CBA officials said.

The convention puts together 335 publishers, record companies and other suppliers in 1050 booths with representatives of book stores catering primarily to evangelical Christians for a week of promoting, ordering and education. More than 8,700 visitors had registered by noon yesterday to inspect paraphernalia ranging from Bibles and greeting cards to nativity scene cookie cutters and evangelical exercise videotapes.

John T. Bass, executive vice president of the CBA, said a survey for the 3,200 store association showed sales were up 6.3 percent last year and have increased 25 percent in the last two years.

Practical books dealing with problems have become best-sellers in recent years, with titles like "What Wives Wish Their Husbands Knew About Women." Such titles continue to proliferate, with the Fleming H. Revell Co. promoting "The Messies Handbook: The Procrastinators Guide to Good Housekeeping."

Recently, the fastest sellers have been books focused on family issues, said Harden Young, president of the CBA. "Four years ago, we never had a book on divorce," he said, noting that his store now carries shelves of books about divorce or child abuse.

Young said the most promising new product is videotape, which is being used for in-store promotion, instruction and entertainment. Videotape appeals to customers who don't read many books, Bass added. The only impediment to the growth of videotape products is the limited number of videotape recorders now in homes and churches.

The trend toward general interest book publishers pulling out of the specialized market was seen in the announcement Tuesday that SFN Companies Inc. of Glenview, Ill., will sell its Fleming H. Revell Co. to The Zondervan Corp., a major evangelical publisher.

Two weeks ago, the CBS Record Group announced the closing of its Priority gospel label because of poor sales, joining MCA Inc., which ended its gospel label earlier.

Young said the secular companies may be experiencing difficulties marketing to the small evangelical Christian market, though Zondervan President Peter Kladder said he believes secular publishers remain committed to the religious market.

However, Robert Fuson, corporate comptroller of SFN, said his company's decision to sell the line was based on inadequate economies of scale, which meant profit margins were too thin for SFN's liking. He acknowledged, however, that Zondervan may do quite a better job of marketing Revell books.

CBA projections say Christian literature sales will continue growing for at least a decade, both because of burgeoning interest from its primary customer base and because direct marketing may be able to reach a largely untapped market.