American Telephone & Telegraph Co.'s new chairman, Charles Lee Brown, has put the goal of improved relations with Washington at the top of his priority list.

Brown, who today succeeds John D. deButts as chief executive of the nation's largest business enterprise, said in an interview that he is making himself "available" to members of Congress, the Carter administration and the Federal Communications Commission in an "effort to reach a consensus among the various parties, so we can find out what the rules will be."

During several Washington meetings earlier in January, this conciliatory approach to government policymakers began even before Brown took over at midnight as the 12th chief executive in AT&T's century of business operations.

"Each of the parties has expressed a point of view, the rhetoric has all been stated, so let's get down to a solution," Brown said in an interview last Friday, made with the understanding that it wouldn't be published until this morning.

On the surface, at least, Brown's statements appear to indicate a new direction for AT&T's senior management. Under former chairman deButts, the company sought to halt a trend in federal regulation and court decisions that have permitted more competition in both intercity telecommunications services and equipment that can be connected to the nationwide Bell System.

Having failed to win congressional approval of legislation supported by AT&T that would have continued a government-blessed monopoly in such markets, Brown said the company today accepts a competitive business environment.

"Now we have a world in which we need to carry out our franchise responsibility [universal telephone service] while at the same time competing with others that want to get more profitable aspects of our business," the AT&T chief declared.

But Brown cautioned that the move to establish competition for such a huge market -- AT&T's sales last year were $40 billion -- "has never been encountered before on this scale."

Basic questions about what types of AT&T services will be open to competition remain to be answered, but in the midst of such uncertainty, competitiors are moving into the business and "I see no reversal," Brown added.

House and Senate committees are working on legislation that would rewrite the Communications Act, by defining the limits of competition for broadcasting as well as telecommunications. Another giant firm, International Telephone & Telegraph Corp., recently was authorized by the FCC to begin intercity telephone service for large users, for example.

While ITT and other potential competitors such as International Business Machines Corp. are seeking to enter the business of providing domestic telecommunications services, AT&T itself is attempting to win FCC approval to offer a data transmission service.

Opponents of this plan say a 1956 consent decree prohibits AT&T from offering a data business but IBM -- for one -- is supporting the telephone company and arguing that the consent decree should be changed to allow the proposed new competition in a market where IBM also has an interest. If high-profit business is taken from AT&T, there is the question of what happens to consumer rates in rural regions where costs now exceed revenues.

Such are the problems now facing the federal government today, which also has a major antitrust case pending against AT&T. The antitrust suit alleges that the firm sought to prevent competition from a monoply position and seeks a separation of AT&T from such subsidiaries as its manufacturing operation, Western Electric; Bell Telephone Laboratories and regional operating companies such as Chesapeake & Potomac Telephone Co. in Washington.

Brown, a 57-year-old Richmond native, has moved up through the AT&T ranks in traditional fashion, having started in long distance operations at Hartford, Conn., after World War II. He became president of Illinois Bell in 1969 and AT&T vice chairman-chief financial officer in 1976.

Selected by deButts to be his successor, Brown said of his former chief that "he's obviously more outgoing... I'm perhaps more reserved... but we have much the same background and differences will develop as I inhabit this seat."

Under deButts, Brown was given the responsibility of directing perhaps the largest major management shift in history in recent months -- a substantial change in the way AT&T operates. Since the firm began, its organization had been divided by functions -- one department for installations and repairs, another for orders, collections and bills, for example.

Now, under the twin challenges of technological revolution and competition, Brown has restructured AT&T top management to meet demands of different types of services or markets -- such as residential and business.

One Wall Street analyst, impressed with Brown's performance as chief financial officer and in the reorganization drive, described the new AT&T chief as "a real intellectual and sharp as a tack... a guy young enough so that all the major problems the company faces over the next seven to eight years -- the transition from monopoly to competition, the antitrust case which they have to fight tooth and nail -- will come under the leadership of Brown... and it is hard to think of someone better qualfiied."

Another assessment of Brown is that in the past "he's had the reputation of being aloof." In the interview here, at the Bell System's Manhattan headquarters, Brown said comparisons of himself with deButts come up naturally in many conversations but there is not "much litany of differences between us."

On other topics, Brown said:

In the Justice Department's antitrust case, "we can demonstrate that the monopoly of previous years was not acquired by some illegal means but by the consensus, encouragement and direction of federal and state regulators." Noting government complaints about AT&T reluctance to turn over certain documents, Brown said that many government agencies similarly are refusing to turn over documents the Bell System contends will prove its case.

Another priority of his stewardship will be "to make sure that nobody thinks this is going to be just another competitor scrambling for business... service-orientation" will remain a fundamental precept.

On a long-term basis, growth in profitability will be about at levels of recent years so that capital can be acquired for construction programs. AT&T sees an economy somewhat stronger than predicted by many forecasters for 1979.