Continuing its growth as a real estate conglomerate, Merrill Lynch Realty/Chris Coile Inc. has acquired Snider Brothers Inc., a local realty firm for 22 years, for an undisclosed sum.

Snider Brothers, which has dealt mainly in home sales in Montgomery County and Northwest Washington, now has six offices and about 150 employes. Four of the offices will stay open as Merrill Lynch/Chris Coile offices, and all the the employes will remain after the merger, said Snider Brothers President Robert Snider.

Snider said the depressed housing market was not the cause of his firm's decision to merge into the Merrill Lynch realty company.

"It's the direction of the real estate business in the 1980s," Snider said. "No matter how good [smaller firms] are . . . the services can best be provided by large companies."

The real estate industry in the past has been dominated by small, local firms, but the larger firms have started to take more of the market in recent years. Sears, Roebuck & Co., for example, last year acquired Coldwell Banker & Co., which already was the country's largest independent real estate brokerage. Real estate transactions are to be part of the "financial supermarket" concept that Sears is creating.

Members of smaller firms have feared it will be difficult for them to compete with the kind of services a Sears or a Merrill Lynch can offer and that more and more agencies eventually will be taken over by the giants. A firm like Merrill Lynch would have the resources to develop and offer new kinds of "creative financing" for clients, a crucial element in home sales with today's high interest rates, real estate experts note.

Merrill Lynch started several years ago to acquire insurance companies and real estate firms, including the purchase of Washington's Chris Coile Realty in early 1980.