It's potentially the most revolutionary piece of TV technology since the VCR. President Clinton thinks it could change what a generation sees on television, shielding children from a culture of violence. And after years of debate, the V-chip, a little bit of silicon destiny, is finally here.

Except that hardly anyone outside of official Washington seems to have noticed. Parents trolling the TV section at the Wal-Mart in Germantown during the weekend weren't aware that the program-blocking technology is now almost as ubiquitous as stereo sound on new sets. Retailers around the area report the same level of consumer demand: zero.

The V-chip -- which allows parents not only to screen out violence (hence the V) but also offensive language and sexual situations -- now comes as standard equipment on many new TVs. V-chip-equipped sets have been trickling into stores in the past two months; by Thursday, federal law requires manufacturers to make half of all new TV sets V-chip-equipped. By Jan. 1, every new set bigger than 13 inches has to have it, the law says. Set makers say they're meeting or exceeding Washington's deadlines now.

The timing of the technology's arrival seems fortuitous. Coming just after the shootings in Littleton, Colo., violence in TV programs and movies is under renewed scrutiny in Congress. The V-chip, President Clinton said when the 1996 law mandating it was passed, could "put the remote control back in the hands of parents." In an interview, William Kennard, Clinton's appointed chairman of the Federal Communications Commission, called it "a high-tech tool for parenting in a high-tech age."

So far, however, the V-chip seems to be causing a stir mostly among those involved in the political battle to make it required equipment. At Best Buy's huge Rockville store, "no one has asked for it," reported a harried clerk. Salespeople at a Myer-Emco outlet in the District and a Circuit City store in Tysons Corner weren't initially sure what the V-chip was when asked about it.

"To be honest, none of the manufacturers told us we were getting it," said Paulo Teixeira, manager of the Pro Video outlet in Glover Park. "We had to get a call from The Washington Post to find out" it was standard in new models.

The widespread availability of the device -- an integrated circuit -- has prompted little media attention. Set makers haven't advertised it, though the Consumer Electronics Manufacturers Association says it is designing a sticker and a logo to alert buyers. The cable and broadcast industries, working with family-advocacy organizations, say they'll eventually air public service announcements.

Many people seem vaguely aware of the device, but the details are more elusive. In a nationwide survey of 1,001 parents earlier this month, the Kaiser Family Foundation found that 77 percent said they would use a V-chip to block shows they didn't want their children to see. But far smaller percentages understood the TV rating system, which is critical to understanding the V-chip.

The chip works in concert with those ratings, the little black-and-white symbols ("TV-PG," "TV-MA," etc.) that the networks began flashing on the screen at the start of their shows in early 1997. The V-chip scans these ratings -- which are electronically embedded in television signals -- and blocks shows based on a ratings threshold that parents set in advance.

Grabbing a remote control and pointing it at a new Sony television, Pro Video's Teixeira showed how it's done. Choosing "parental control" from an on-screen menu, he first punched in a four-digit personal identification number -- a secret code designed to foil children who want to defeat the blocking mechanism. After switching the "parental lock" feature to "on," he began selecting the ratings he wanted the chip to block. His choice: "TV-PG-D."

That means any show that is rated PG or beyond and contains suggestive dialogue ("D") won't appear on the set. And just like that, an afternoon soap opera went blank on the screen, replaced by a little symbol of a lock and the word "BLOCKED."

The chip can also be set to block R-rated movies, or shows that carry no rating at all, such as news, sports and public affairs.

The concept gets a strong endorsement from parents perusing the aisles of the Germantown Wal-Mart. "For her, at her age, it's not useful now," said Terry Hedrick, glancing at his infant daughter, Cassidy. "But I can see it in a few years."

"There are a lot of things you just don't want kids watching," said Steve Pinkley, at the store with his 3-year-old granddaughter, Martha. He wonders, though, whether there's any device that kids can't beat. "She's already on the computer and knows about e-mail," he noted. Neither Hedrick nor Pinkley was aware the technology is now available.

Given that many people can't even program their VCRs, it's questionable whether parents will ever be chip-hip. In its survey, for example, the Kaiser Family Foundation found that only 3 percent of adults could correctly identify the meaning of the rating "FV," which stands for fantasy or cartoon violence. And only 2 percent knew what "D" stood for.

If it does come into widespread use, the V-chip conceivably could alter the television landscape -- and the way in which children relate to it.

"To the extent that there are parents trying to limit access to violence or inappropriate content, I think it could make a pretty substantial difference," said Vicky Rideout, who directs the Kaiser program that studies the public health impact of the entertainment media. "I think it could stop young children from being bombarded with violent images in cartoons. I think it might encourage families to seek alternatives and build audiences for more nonviolent and educational programs."

A violent or bawdy show that is automatically blocked by many households would likely lose advertisers -- and quickly go off the air. But some observers worry about the opposite effect: that the V-chip might give producers an excuse to turn up the sex and violence because families now have the means to block it automatically.

"We don't think that will happen," responded Dennis Wharton, spokesman for the National Association of Broadcasters, which represents TV stations and networks. After the Colorado high school murders, "there is a real sensitivity to the programs we put on. That's not to say we are into censorship, but our sensitivities have been heightened, no question."

Deployment of the chip could come relatively quickly. About 25 million TV sets are sold each year in the United States, according to the Consumer Electronic Manufacturers Association. Since about 10 percent of existing TVs are replaced with new sets each year, roughly half the households in the country could have a V-chip TV in five years (manufacturers say the addition of the technology will add little, if anything, to the cost of a new set).

Yet recent history suggests that many V-chips will never be used.

Under a 1984 law, cable TV companies are required to offer channel-blocking "parental lock boxes" to subscribers. Industry-wide figures are not available, but several people in the cable industry say there have been few requests.

What's more, the V-chip in a slightly different form proved to be a flop in a test last year. Tri-Vision Electronics, a company based in Toronto, marketed so-called "outboard" V-chips, which retrofit old TVs to block programs. Despite spending $3.5 million to promote the device in Chicago, Nashville and Indianapolis last September, Tri-Vision got an underwhelming response: It sold just 870 units.

"We asked people if they were interested in a device that could screen out programs they didn't want their kids to see, and a significant majority said yes," said Todd Grunberg, Tri-Vision's vice president of marketing. But the details of the rating system tended to confuse would-be buyers, discouraging them from making a purchase, he said. Tri-Vision is now concentrating on licensing its device to manufacturers, such as Sharp Electronics, for incorporation into their sets.

"We still have faith in the technology," Grunberg said, "but this isn't going to be a short exercise. It's going to be a long one."