Federal Communications Commissioner Chairman Charles D. Ferris, in office for one month, yesterday endorsed the agency's policy in recent years of encouraging competition where possible in the telephone industry.

"Where the free enterprise system can work, where the competitive environment can work, I think it should be permitted to," Ferris said in an interview yesterday. "There are places for monopolies and there are places for a competitive environment, and you have to make determinations on an ad hoc basis."

He said there wasn't anyone, particularly anyone who has traveled abroad, who wouldn't have high praise for the service provided in this country by the American Telephone and Telegraph Co. network.

"It's high quality and dependable," he said. "You want to keep that quality of service and that dependability, but you don't want to prevent a competitive environment where it will have no adverse effect on either of those two dimensions and additionally will provide protection to the consumer with respect to rates and options.

"That's exactly what the existing policy of the commission is, and I . . . feel very comfortable with it," he added.

What attracted the long-time legislative aide to the FCC - and he says it's the "only agency" he had any interest in - was the commission's involvement in common carrier issues and not what some believe to be the more glamorous broadcast responsibilities of the FCC.

"The broadcast issues are very important and significant," Ferris said, "and I think the electronic media has tremendous effect upon society . . . but the issues that I find the most exciting are in the area of telecommunications and common carrier.

"I think the types of decisions that will be made at the commission over the next several years will have significant impact on how our society is shaped 30, 40 years from now," he said.

Ferris contrasted the burgeoning technology in telecommunications the commission will be addressing with the energy problems he had some involvement with as general counsel to House Speaker Thomas P. (Tip) O'Neill Jr. (D-Mass.) this year and during his 13-year stint as a senior aide to Senate Majority Leader Mike Mansfield.

"In energy," he said "we have dwindling resource and we're attempting to make determinations as to how one would allocate it so as to best serve the public.

"Here at the commission what we're having is a mushrooming technology . . . and we'll be making decisions and choices as to how they fit and which one we'll emphasize."

Those decisions he explained will guide the whole nature of communications, how and what types of information will come into one's homes and businesses.

"I don't think it's Buck Rogers to conceive of a system in the very near future of homes and certainly businesses having not only voice communications with each other but access to data banks, even wide communications," he said. As an example Ferris mentioned computer terminals in each home and business for translation ranging from banking business to ordering groceries.

"There are an infinite number of options," he says, "Your imagination can become very excited just by the prospects."

Ferris has made no decisions about a possible reorganization of the commission, but has decided to take steps to beef up the planning and forecasting capabilities of the agency by expanding significantly the Office of Plans and Policy.He also hopes to establish within a year an office of chief economist; the FCC is one of the few regulatory agencies without one.

"I think it makes sense to have an entity or shop that could make independent determinations of the economic implications of our decisions," he said.

A man who has won praise from within the agency for his quick grasp of the complicated issues, Ferris, 44, said that a lack of experience in communications hasn't hampered him on the job.

Once a maritime lawyer, Ferris said, "I've come to realize that once one learns the vocabulary, sorting out a complicated factual situation applies to any field, and communications is the same way. It's like the old story about the guys who used to tell jokes at the luncheon club. They told them so often that they used to tell them by numbers. Everyone used to laugh at number 43.

"Well, I'm sort of asking what number 43 is and seeing if I want to laugh. Maybe the joke isn't funny today as when originally told, and that's all the process is about - just having sufficient confidence to be able to say 'what do you mean by that?'"