If a mailman can't deliver, he whistles for a 'Nixie'

Kick, if you must, our old friend ''the US Snail Service.'' But you, the complainer, like hundreds of thousands of other mail users, may be part of the problem.

Take, for instance, the airmail envelope from England addressed simply to ''Frank, 64402553'' that landed in Boston's main post office recently. The neatly penned four-line return address on the reverse side proved the writer was no careless correspondent: This was clearly a teaser, a tongue-in-cheek test of the controversial nine-digit zip code which the Postal Service is eagerly waiting to implement as soon as Congress flashes the green light.

Thomas Doherty rose manfully to the transatlantic challenge. As New England's only ''Nixie'' clerk, he is one of a special breed of postal employees who use their heads instead of their feet to deliver mail. Envelopes and packages bearing incomplete, incorrect, or illegible addresses are grist for the Nixies' mill. Mr. Doherty alone solves 1,200 whodunits a day, unscrewing the inscrutable. Doherty recognized at once that some joker in London was pulling his leg. He detected that what the mailer had done was add the addressee's post office box number to his Massachusetts zip code.

So Doherty ferreted through a directory of post office box numbers for Frank's Cape Cod address. He penned it in and plopped the envelope on top of the neat stack of solutions he was rapidly piling up that morning.

These Sherlock Holmes jobs are so sought after by postal employees that the clerks who land them are usually those with plenty of seniority and experience. How long has Doherty been with the Post Office? ''Seventy-two years,'' he replies with a straight face, then almost falls off his chair laughing. It just seems like 72, he says. It's really only been 29 years, and a Nixie only the last two or three. ''When you're having fun you really don't count the days,'' he says. ''It's the job I really always wanted.''

Even the Postal Service doesn't know for sure how the term ''Nixie'' got started. The slang ''nix'' stems from the German ''nichts,'' meaning ''nothing.'' Perhaps in the early days ''Nixie'' may have been a label on a box or pigeonhole for undeliverable mail.

Nixies are only required to research the destination of priority mail such as registered, certified, COD, special delivery, parcel post, or foreign. But they also have time to have a heart. And occasionally romance gets to them.

The other day a fellow sent a postcard from France. He had a girl's name and phone number but couldn't remember her address. He appealed to anybody in the post office who received his card to help him locate her. With the aid of a bookcase full of telephone and street directories, Doherty had no trouble tracking down the girl in Wellesley College, Wellesley, Mass.

As a Postal Service bloodhound, one of detective Doherty's more spectacular rundowns involved an envelope addressed only to a man with a Polish name, with no other address than ''Massachusetts.'' Stuck on the reverse side was a picture torn from a magazine showing a man standing in front of a tenement house with the number 232 on it.

''I looked in the Boston street directory,'' Doherty explained, ''and found a party by that name who lived at 232 West Fourth Street. I sent it out and it never came back, so it probably got there.''

Tom Doherty delights in wrestling to the mat this kind of mail that never returns. What drives him up a wall is mail that keeps coming back like a boomerang. ''It gets me upset,'' he says with a little chortle. Which explains why he is waging his own private war on computerized mail.

Every week, sure as clockwork, he gets from the City of Boston parking tickets bearing wrong addresses. ''They don't correct them,'' he complains, ''and they'll never collect a dime from those people because the drivers don't even know they have tickets. I hate computers!'' he murmurs in a low, mock threatening voice. He raises his only weapon, his ''Insufficient Address'' stamp , bangs it down, and sends the envelopes back to City Hall.

In between playing Cupid and battling the Boston Traffic Department, Doherty solves a lot of address problems just by his extensive fund of general knowledge.

Here's a letter addressed to Brownsville, Ma. He knows there is no such place in Massachusetts. It was mailed in Maryland. He knows there is a Brownsville in Maryland, so he puts the proper Maryland zip code on it and sends it on.

Foreign mail is often incomplete. Here is a correspondent in Australia writing to someone in Chippewa Falls, USA. Doherty doesn't even have to stop and think. He knows that's in Wisconsin.

Here is one that requires more ingenuity: An envelope addressed to someone on Wake Forest Road, Raleigh. It doesn't even say USA. ''Raleigh, of course, is the capital of North Carolina,'' Doherty muses. ''And Wake Forest University is in North Carolina. So I go immediately to my zip code book and look up North Carolina and sure enough I find Wake Forest Road and the zip code for this particular street.

''It's been 19 years since the zip code system went into operation. And make no mistake. Zip codes do put zip in mail delivery and a lack of a zip number definitely slows it down.

Postal people don't have time to read like other people - from the top down. They read from the bottom up. Operators of mechanical sorting machines have only a split second in which to glance at the last line on an envelope, because 3,600 pieces of mail whiz past them every hour.

Though zip coding is voluntary, 97 percent of all mail today is zipped. The remainder has to be processed manually, which slows the mail down considerably.

But if zip numbers are illegible, they cause their own turmoil. ''If you're in Boston and have a piece of mail to go a few blocks away to, say, Park Street, '' Doherty says, ''the zip number begins with 021. But if you make your zero look like a 9, the letter is going to go to San Diego. That happens a lot.

''The way European mailers pen their numerals can also cause confusion. ''Their '7' often looks like a '1' to us,'' Doherty says. So instead of going to 07 (most of New Jersey), many overseas letters are misdirected to 01 (much of Massachusetts).

Doherty could do without the mistakes that stem from those two-letter abbreviations for states that came in with mechanized sorting and the zip code. ''Here's a piece that was mailed in Texas and going to Mississippi,'' he says. ''But because the MS was illegible and mistaken for MA, it came here to Massachusetts.

''He says if you don't have the zip code, ''it is better to write out by hand the full state abbreviations we used to have,'' such as Miss. and Mass.

Other reasons for misdirected or undeliverable letters are people who don't file a change-of-address notice, and bulk mailers' failure to keep their mailing lists up to date.

Judging from the number of times he has received mail for one particular party, Doherty figures that ''this person graduated in 1971, and for 11 years his school has been sending its mailings to the same wrong address. They'll get this one back,'' he says with a good-humored grimace, ''but they'll do nothing about changing their lists.

''Challenging as it is, Doherty says he wouldn't want to have any other job. Nixies everywhere seem to share his enthusiasm.

William R. Duval Jr., manager of the Boston Claims and Inquiry Division, explains that in Boston the Nixie does all his super-snooping on the outside of the envelope. Only dead-letter clerks at the other end of the room are authorized to open mail for the purpose of finding some clue as to how to forward it.

These other clerks handle so-called ''loose in the mail'' items that fall out of their envelopes: checks, keys, eyeglasses, contact lenses, films, cassettes, etc. in addition to wallets and purses that are believed pitched into mail boxes by pickpockets and thieves.

But in Portland, Ore., the Nixie there, George Stone, also handles ''loose in the mail'' items. He told the Associated Press that even without return addresses, he is able to match about one out of every 10 letters with their envelopes. ''I matched one today and the only reason was that the writer had a cute little curlicue on her Ms,'' he says.

Checks, of course, have to be shepherded back to their writers. It's a snap to do so because the bank's name and town are printed on them and often the check writer has taken care to have his own address printed on, too, which Duval says is a smart idea. It speeds up delivery.

The biggest check Mr. Stone ever processed was for $1,307,065.05. ''I remember it because the 5 cents stuck in my mind,'' he says.

The Portland Post Office had quite a go-around with unsealed envelopes and Mt. St. Helens ash. Two years after the 1980 eruption, ash is still filtering through the postal system.

All Nixies agree that you the people could make their work much easier by using return addresses, correct zip codes, and writing in a legible hand. You could also save yourselves and other taxpayers a lot of money. Duval says the budget for running his department of 33 clerks and two mail handlers runs to $ 750,000 a year.