W. Bell & Co., the Rockville-based catalogue-showroom chain, yesterday declared a 50 percent stock dividend that is expected to significantly increase trading in the company's shares.

The stock dividend was announced at the company's annual meeting, at which Chairman Walter Bell disclosed the chain plans to open at least three, and possibly four, more units next year.

Bell said the new showrooms will be in existing markets, including the Washington area and Chicago, but did not identify the sites.

The steadily growing chain pays no cash dividend on its stock, but previously paid two 5 percent stock dividends and declared a 20 percent stock dividend last year.

"What this really means is that if you had purchased 100 shares of W. Bell & Co. stock when the company went public in July 1972, and you retained that stock until this new 50 percent dividend, you would own 198 shares without having made any additional investment," Bell told shareholders.

The 50 percent stock dividend is equivalent to a 3-for-2 stock split, Bell noted. But a stock split would have required amending the company's charter, a costly step not needed to pay a stock dividend.

The Bell company now has 1.25 million shares outstanding and will have just under 1.9 million shares after the stock dividend is paid on Dec. 11 to shareholders of record Dec. 2.

Martin Pfeifer, vice president for finance, said the dividend is expected to broaden the market for Bell's stock by increasing the number of shares in public hands. Almost 80 percent of the shares are owned by Bell family members and other company officials.

The stock is traded in the over-the-counter market and has drawn more investor interest in recent months since Kidder, Peabody & Co. began making a market in the shares, Pfeifer added.

Chairman Bell said the big stock dividend was made possible by the company's growth. From six showrooms, sales of $15.8 million and profits of $310,000 a year when it went public, Bell grew into a $107 million operation earning $2.5 million profit from its 15 showrooms last year.

Fredric Bell, senior vice president, said the chain has seen no signs of weakness so far in pre-Christmas business. Sales of jewelry--the company's best selling and most profitable merchandise--and big-ticket electronic items are holding up well, he added.