CBS, Inc., announced today that it will make a major effort to become an important motion picture producer and may also set up its own distribution network for feature films.

CBS made a fledgling move into the motion picture business in late 1979. The first release from that film division, "Back Roads," starring Sally Field And Tommy Lee Jones, is being distributed by Warner Brothers and will open Friday at about 800 movie houses.

CBS president Thomas H. Wymann said the major broadcasting and leisure products company believes that the motion picture business can "be the largest new growth area" in the company for the next few years. In a statements, Wyman said CBS plans to make a "major long-term committment" to motion picture production and distribution.

Last year, CBS had revenues of $4.1 billion and profits of $193 million. Profits fell 4 percent on the year.

Observers said the CBS move is unusual because it comes at a time when many independent producers are cutting back on their activities. ABC, for example, announced two years ago that it would enter the movie production business, but so far had not make a feature film.

In recent years, as the cost of distributing movies has risen, distribution of major films has been concentrated among six major studios -- Warner Brothers, United Artists, Columbia Pictures, Universal, Paramount and Fox.

The CBS annoucement was short. Although it said the company plans to make a major investment in the activity, it did not say how much. Wyman, who was enroute from the West Coast when the statement was released, told analysts last month that the company planned to make $40 million to $50 million in development investments during the next year, but did not say what CBS businesses would get what portion of those investment funds.

At the same meeting, Wyman said it was "neither possible not appropriate" to estimate the capital needs of the film production business. He said then that CBS was at its first stage, with the imminent release of "Back Roads," and said the number of films it would do, but said it would do so slowly.