MARRIED WOMEN may not have found their place in the sun, but they're gaining a place in the phone books-which may have more practical worth. The American Telephone and Telegraph Company is finally encouraging its subsidiaries to let husbands and wives list both first names in telephone directories without any monthly charge. The Bell System won't get into the delicate matter of which name comes first; it will be up to each couple to decide between "Doe John & Mary" and "Doe Mary & John." Either way, the dual listing will help Mary Doe's friends and acquaintances get her number when they don't know her husband's first name.

Locally, the Chesapeake and Potomac Telephone Company has not yet changed its rules. If Mrs. Doe wants her own listing here, she still has to settle for a separate line in the phone book - at a monthly cost of 30 cents in the District, 40 cents in Maryland and 80 cents in Virginia. C&P is planning to seek a rate change in Maryland to allow dual listings with no monthly charge - but with a one-time processing fee of around $8. D.C. and Virginia spouses might wonder why they aren't being offered equal opportunities.

The dual listings are just part of Ma Bell's new regard for customers' various identities. Some phone companies now allow listing of nicknames, such as - to invent an example - "Mondale Walter F. - Fritz." That is good news to anyone who has ever tried to ring up that old college buddy known only as "Meatball" Jones. Once this sort of thing catches on, though, the good Lord only knows where it's likely to end. What about listings for swingers ("Doe John & Mary - Buddy & Toots")? And what about children, or rock groups ("White Snow & Sleepy, Sneezy, etc.")? And what about people who - to put it vaguely - share the same phone but have different last names?

The new styles could make future phone books quite interesting. We suspect, though, that this revolution could bring on its own demise. Mary Doe may enjoy hearing from her acquaintances - but she will also be getting more calls from peddlers of magazines, light bulbs, country land, cosmetics and the like. After a bit of this, she may have more appreciation for the old rule, "If you can't stand the heat, get out of the book." Then the issue will be whether spouses may be unlisted under their own names.