HARRISBURG - Every Wednesday afternoon, a committee meets in an obscure, five-story, built-by-the-lowest-responsible-bidder office building well away from downtown and the publicity glare of the Capitol.

Its mission: Keep Pennsylvania highways clean.

It's dangerous work. Double entendres creep in the shadows. Innuendos drop from the ceiling like cinder blocks. And behind every filing cabinet is a DV8.

Call them the Plate Police, if you must, but it is with a profound sense of gravity and urgency that the committee's four members - balanced by gender, lifestyle, and generation - sift through suspect applications for personalized license plates. The Pennsylvania Department of Transportation receives about 300 requests for these vanity plates every week, and about five of them are kicked upstairs to the committee.

"There are two men and two women," says Anita Wasko, director of PennDot's Bureau of Motor Vehicles, who says they are employees of the bureau whom she prefers not to identify. "Each brings his or her own set of experiences to the table. In addition to all the databases and reference tools, they develop an innate sense of different letter and number combinations."

This business of separating profanity and vanity is not for the naive or the squeamish. You have to know that there's something amiss with QUADPLAY (foreplay); that 5 looks like S, making A55 unacceptable; that X3SLARO resembles something else spelled backward; and that a lot of people are going to figure out PNISNV and write irate letters to PennDot.

Phonetics are critical. Such combinations as 4-NIC-8 and JENATALS warrant speedy rejection. Foreign languages also come into play, even if - like the French word for what the poodles leave on the Champs-Elysees - the plate looks innocent in English.

The ladies and gentlemen of the committee come to their deliberations well-armed. They have slang dictionaries, an acronym database, foreign-language dictionaries, and an array of digital reference tools to screen out not only inappropriate sexual material, but also references to drugs, gangs, ethnic slurs, and violence.

But the most potent weapon is Table 0566, known to insiders as "The No-No List" - a growing compilation - now numbering nearly 300 pages and 10,000 entries. From ABOOGER to ZUCKU, the list is a compendium of bad taste - a field guide to the less attractive recesses of the human cranial vault.

There are some easy calls in Table 0566: TUSH, TOUCHME, PISTOF, LEZDOIT, HELLYES, and almost anything beginning SEX.

Unless, of course, your last name is Sexton. Here is a mine field of ambivalence that is the most taxing for the Plate Police. They've approved several versions of TOPLESS - but only for owners of convertibles. And despite the prohibition on drug-related inferences, there's a lawn-service owner driving around with GRASS. If someone named Joe Hooker ever applied for HOOKER, he'd get a fair hearing, and anyone named Sexton could probably get SEXTON with no questions asked.

There are about 276,000 Pennsylvania vanity plates on the highways, accounting for about 2 percent of all vehicles. About 15,000 new ones are issued each year, with a one-time charge of $20. They bring in $240,000 a year. Vanity, thy name is Profit!

Nationwide, there's a virtual bonfire of the vanities. About 250 million vehicles sport license plates that, in a maximum of six or seven letters and numbers, display their owners' professions, favorite sports teams, religious beliefs, pet preferences, marital status, and hundreds of other personal matters right above their exhaust pipes.

George Snoke of Mechanicsburg has SSSSAX on his tan Hyundai Santa Fe SUV.

"I've been playing the tenor sax for 62 of my 72 years," he says. "Right now I'm playing in the town band and a church orchestra. In 1985, I decided I wanted to get a personalized plate. I asked for SAX, but it was taken. Then I tried SSAX and SSSAX, but they were all taken. So was TNR SAX. So finally I hit it - SSSSAX!"

Luckily, the only vowel in his request was an A and not an E. No need to kick it upstairs to the committee, presumably.

"I've had it ever since, and I really like it," he says. "It says something about me, something I'm proud of, and something that's important to me.

For people like Snoke, the license is the message. For bureaucrats, it's a war of words in the fast lane, and every state has a form of the Pennsylvania Plate Police to ensure that plates are roadworthy. This year, Colorado's unit had its hands full with a woman who was a vegan and wanted to express her undying affection for bean curd with a vanity plate that read ILOVETOFU. She was turned down.

In Pennsylvania, the buck stops with PennDot's Wasko. If the Plate Police can't agree on a request, they send it to her.

"I only get one or two a year," she says. An example? "Well, recently, there was one. . . . I can't bring myself to say it. . . . Should I say it? . . . No, I can't. . . ."

Finally, she defaults to a bromide. "Some things are best left unsaid."