It's not a flashy Zip code, like Potomac's 20854, or full of huge estates, like Foxhall Road's 20016. No, 20815 is a discreet, tasteful Zip code for people who have arrived, but don't necessarily want to advertise the fact.

But the 192 millionaires who live in 20815 make it one of the top 20 richest Zip codes in the country -- along with five other local Zip codes: 20016, 20854, 20007, 20008 and 20817, according to "Who's Wealthy in America." The 2,000-page, $295 guide to the mega-rich, published today by the Taft Group, lists the names of 46,280 millionaires, multimillionaires and billionaires, and their addresses, phone numbers, ages, hobbies and political contributions.

It's the kind of information most of the residents of the exclusive Chevy Chase neighborhood would rather keep to themselves, thank you very much.

But Joanne Wood already knows the inner life of the men and women of 20815. She knows their habits, their hobbies and their history. She delivers their mail.

Wood, 31, who lives in Greenbelt (20770), has been one of the 42 mail carriers of the tony 20815 for five years. For $28,900 a year, she delivers mail to the 243 houses in her route. She arrives at the Bethesda-Chevy Chase carrier annex at 6:30 a.m. to sort that day's mail, load it in a 16-year-old Jeep and walk the five-mile route to deliver an average of 16 pieces of mail per house.

You can tell a lot about 20815 from the mail Wood throws into the address slots.

"People with money get a lot more mail. They can afford every subscription," she says. "Not many people are going to be getting Fortune or Money magazine unless they've got money. You get proxies galore. And dividend checks -- lots of dividend checks."

Joseph King, acting manager of the carrier annex, says, "We've always claimed Bethesda-Chevy Chase is one of the hardest areas for a letter carrier because it's generally door-to-door delivery with large amounts of mail." Most carriers don't like door-to-door delivery; they like the more accessible curb-side mailboxes.

But 20815 has an upside: The homeowners tip, a sort of reward for taking the time to chat. "Technically, there's no such things as tips," says King, "but, in general, they're very generous to their mailmen at Christmastime." (Translation: An occasional $100 bill; $10 and $20 are "very common.")

The downside is extra picky homeowners -- and the dogs, especially the small, nasty ones. "There's a lot of yip-and-yappers up here," says King, who gets three to four bite reports a year. "It's the little ones that get you. They nip you and run back inside."

Life in 20815 is good. Very good. Tucked just beyond the District line in Maryland, the houses are beautiful, the trees lush. People may say they live in Chevy Chase, but if their Zip code isn't 20815, which includes Chevy Chase Village and Kenwood, it's just wishful thinking.

It's the home of diplomats, doctors, lawyers, politicians and media celebrities. George Will lives in Chevy Chase, and Arch Campbell, David Brinkley, Sandra Day O'Connor, B.F. Saul, William Bennett, J.W. Marriott Jr., William Safire and Tom and Joan Braden. Spiro Agnew and H.R. Haldeman used to live in the same subdivision. Hubert Humphrey had a house there; George McGovern was his next-door neighbor.

"It's the address," says Wood. "You could get a nicer house somewhere else, but people want the Chevy Chase address. For the same money you can get three acres in Potomac, but it's not the same."

She almost sounds like a real-estate agent: She can tell you who lives where and how much they paid for the house. "$200,000 is a cheap house in Chevy Chase." In the Village, they start at half a million.

She points to a big gray house with pink shutters. "Old George lives there," she says, referring to columnist Will. The yellow house a couple blocks away is Will's ex-wife's. David Brinkley has a huge brick two-story with two stone greyhounds guarding the entrance; it looks like the other 50-year-old homes on the block, but if you look closely you can see it is brand new. "He couldn't find anything he liked, so he just had this built."

She weaves expertly through the quiet streets past Arch Campbell's house ("That's what watching movies for a living will get you") and then suggests a run past Bill Bennett's white two-story.

"We can go see the drug czar's house. Not huge, but not shabby. The Secret Service is in front of his house all day long, but he's away, so they're probably not going to be there."

Wood reels off prices: That house sold for $2 million, this one's on the market for $2.5.

The 20815 Zip code is a gold mine for advertisers, who have seized upon marketing data bases for their direct mailing.

R.H. Donnelley, one of the country's largest consumer information data banks, reports that in 1989, the 20815 Zip code had a median household income of $64,457, almost $40,000 more than the average American household. InfoMedia Corp. of Falls Church gets even more specific: Almost half of the 16,000 households in 20815 have incomes of more than $75,000, 60 percent of the homes are mail-order buyers and 54 percent have "highbrow" interests -- wine, music, the arts.

"These people have money, but they don't flash it too much," says Wood. "You can tell a lot if you look. You have a nice house and you have a house that's well kept. You've got a house that costs a lot of money to begin with. Then you can see everything they've put into the house, beyond just the structure -- luxuries. They have landscapers who come out every week and do this and that. Then you see the cars parked out front."

Most of the houses on Wood's route are two-story brick homes with groomed lawns, flowerpots and decorative wreaths on the doors. There are a few Mercedeses, Saabs and the 20815 "family car": Volvo station wagons. It isn't the richest part of Chevy Chase; it's a mixture of yuppies and older homeowners, who bought their homes before the real estate boom of the past 10 years. Most of the people on her route are "very down to earth. ... Most people don't feel they're above you."

There are a few stay-at-home moms, a lot of two-career couples, whom she rarely sees, and their nannies and housekeepers, whom she does. "That's the only reason they can afford to live out here. They both have good jobs -- two lawyers or a doctor and a lawyer. Two mailman's jobs don't get you in Chevy Chase."

And with that, she pushes a copy of the New England Journal of Medicine and another of Infectious Diseases through the mail slot of one more perfect door of a perfect house and walks across the perfect lawn of 20815.