IF YOU HAVE been looking at the ads, you know that the prices of those machines known as video recorders have been coming down while the prices of almost everything else have been going up. They're still expensive - $800 and up. But enough of them are in use (150,000 or so) and their makers are promoting sales furiously enough to suggest that they are more than just another electronic gadget. Like the television sets of a generating ago, the video recorders are capable of producing major changes in the way we live and in the communications and entertainment businesses.

One version of these machines, in case you haven't seen it, takes television signals off the air, records them on magnetic tape and plays them back on command through your television set. Given the right attachments, it will record one channel while you watch another, record programs while you are not at home, or play prerecorded tapes of, say, movies or Broadway shows. Down the technological road are devices to turn home movies into tape, to run programs backward or in slow motion - and who knows what else? Coming into competition soom with these tape systems will be others based on dics like phonograph records. While these systems won't let you record material off the air, the basic set will be cheaper to buy and the cost of prerecorded discs of movies or symphonies or do-it-yourself programs will be substantially lower and the visual quality somewhat higher than comparable tapes.

It doesn't take much imagination to figure out some of the things that come next: movie-of-the-month clubs, rental libraries, discount stores and so on. But no one is quite sure what all this will do to television and the resurgent movie industry. What if most people decide that, rather than watch what the networks offer, they will program their own entertainment from the disc or tapes they can buy, rent or borrow? Will that be the end of network television as we know it? Or what if people decide to tape programs at off hours and play them during prime time rather than watch the network offerings? The ratings game, in which television is so deeply engrossed, could turn into chaos. And what if all those parents who hate the commercials for sugary breakfast foods were to provide their children with a supply, on tape or discs, of the same cartoons minus the ads? If these or any several other possiblities occured, the role of television as the major supplier of entertainment would be sharply changed. In response the networks might be driven to expand vastly their role as a supplier of news of live events - political, social and athletic - thus beginning to live up to the potential they have never fully exploited.

There are a couple of clouds on this horizon. One is the reverse side of the competitive system that is bringing down so quickly the prices of these new devices; some of the various systems are incompatible and consumers who buy the ones that lose out in the market may be stuck with obsolete equipment, just as some consumers were in the early days of long-playing records. The other cloud is a lawsuit in which two movie-makers are charging that the federal copyright laws are violated when consumers tape things likes movies off the air. They may well be right; the tape-system manufactures are now telling customers that federal law may be broken when copyrighted material is taped. If so, the solution is to find a way to protect the owners of the copyrights without destroying this new tape industry. That might require some legislation by Congress.

So far, neither Congress nor any other arm of government has gotten into this field. When they do, the principle guiding their action ought to be clear. These new recorders, especially when combined with the coming mini-computers and cheap television cameras, can change that home television set into an information and entertainment center almost beyond belief. The government's role should be to remove any roadblock and let it happen.