The American Telephone & Telegraph Co. has recommended substantial changes in the Federal Community changes in the Federal Communications Commission's program permitting the hook-up of a customer's privte telephone equipment to AT&T lines in a written response to a Senate subcommittee's questions.

In a crisply-worded 20-page document. AT&T reasserted its objections to the program which its objections to the program which it said will cause the deterioration of the nation's telephone system and made a score of specific recommendations on quality and enforcement standards which it said will improve the FCC program.

The primary recommendations made to the communications subcommittee of the Senate Commerce Committee were to require the installation of at least one telephone company instrument to single-line customers and allow them to add only secondary personal equipment to ease repairs and line maintenance to require quality controls for privately manufactured equipment and to set up enforcement provisions for non-complying manufacturers and suppliers.

AT&T also termed the requirement that its own equipment he registered with the FCC under the program "wasteful" and urged that the provision be eliminated.

In a letter to subcommittee chairman Sen. Ernest F. Hollins (D-S-C.), AT&T assistant vice president Mickey McGuire added. "No one but the customer pays for this kind of unnecessary and useless regulation."

In a terse critique of the program as it now stands. AT&T wrote. "The program is devoid of quality control procedures in manufacturing. Its design criteria is (sic) still inadquate - a device can be registered without regard to whether it will generate proper dialing signals. It is unenforceable since there are no penalities for non-complying manufacturers and suppliers."

The company urged that the FCC establish basic operational requirements for all equipment to protect consumers from malfunctioning or poorly functioning equipment and to prevent the downgrading of the present nationwide system.

It also citied the lack of maintenance and repair standards as a major failing of the program.