The Federal Communications Commission yesterday said it may change the way local telephone companies assign customers who do not choose a long-distance company under so-called "equal access."

Equal access, mandated by the agreement breaking up the Bell System, allows long-distance users to choose a primary long-distance service other than American Telephone & Telegraph Co., eliminating the lengthy codes customers previously had to dial to reach AT&T's competitors. Currently, customers have up to six months after the start of equal access to make a choice of long-distance service. Those customers who do not make a choice automatically "default" to AT&T.

An FCC official who asked not to be named said yesterday that Chairman Mark S. Fowler will recommend next week that the FCC express serious concern that "defaulting to AT&T is not legal or proper." The FCC then will decide whether or not to change the rule.

If the FCC decides to change the system, local phone companies may be asked to notify customers who do not make a choice that they have been temporarily assigned to another long-distance company. The customer would then have another 30 days to "vote," the FCC official said.