The relentlessness with which the alien invaders attack the earthlings in video games is matched by the speed and intensity with which copiers of popular games attack the innovations of the major makers of the arcade quarter-eaters.

Williams Electronics Inc. introduced its latest entry in the game fad sweepstakes a month ago, and it has already filed two court actions in Canada to get off the market similar games it calls infringements of the basic Moon Patrol game, which it produces under a license from Japan.

The electronics wizards who design the zaps and zooms are increasingly building into their games protective circuitry designed to foil the copiers -- or at least make their task take longer, so the original entrant can corner the market during the few months during which most games reach their popularity apogee. But the original manufacturers have been fighting the copiers in court, too, and a major victory recently won by Williams in litigation about its successful Defender game has opened a whole second defense front, one that is likely to have application well beyond the wars over electronic wars.

Video games are not patented. They seldom represent the kind of technological breakthrough that would warrant a patent, and no one would want to hold up marketing a possibly hot new format for the time it would take to get a patent. The usual line of legal protection is the copyright, covering both the distinctive on-screen look of the game and the unique sounds it generates. In fact, it is common to get two copyrights on the looks, one covering the "attract mode" -- the noise and images that race across the screen when it is not in use, intended to lure in quarters -- and one covering the "play mode" during which the player's own choices of pushes and pulls determines the exact pattern developed on the screen.

Makers of games that copy the original entrants in the market -- or of circuit boards that can be connected to a cathode ray tube to produce a copy-cat game -- have claimed that the constantly changing series of electronic blips cannot be copyrighted because the law requires the copyrighted creation to be "fixed in any tangible medium of expression" and the images are not "fixed." They also question the practice of filing videotapes of games in progress with the Copyright Office as examples of the creation being registered. But a series of court decisions this year -- including rulings from the U.S. Courts of Appeals in New York, Chicago, and Philadelphia -- have rejected those arguments.

The problem for the companies that develop the new games is that it is not too hard for copiers to get around copyrights. By changing the colors or the shapes of the attackers or the defenders, while keeping the basic concept of the way the new game is played, the "me-too" manufacturers can at least begin to make the legal argument that their look and sound is different enough from the one copyrighted.

It is less easy to get around the second line of protection won by Williams from the Philadelphia appellate court. The judges there, for the first time, found copies of the underlying computer program for the games a copyright violation. The issue is a novel one in the courts -- but of increasing importance in the real world of electronic manufacturing -- because of the form in which the program was copied.

There's no question now -- as there was before the 1980 revision of the Copyright Act -- that computer programs can be copyrighted. And in the Defender case, there was what Judge Dolores Sloviter called "overwhelming evidence" that the me-too game's program had been copied. A mistake in early versions of Defender -- a wrong score for destroying a particular kind of alien -- was repeated in the copy, she pointed out, and even a hidden copyright notice was carried over into the copy.

Business programs are normally printed out in text form, and any copy of that text would clearly violate a copyright. But in the games, the program exists in what the industry calls ROM (for "read only memory") chips. The copies were ROM chips, too. ROMs are fine for telling computers what to do, but they don't by themselves convey any meaning to you and me. That means they do not infringe the copyright on the program, the maker of the imitation Defender games argued, because in order to come under the law "a 'copy' must be intelligible to human beings and must be intended as a medium of communication to human beings.' "

The Philadelphia appellate judges refused to buy that argument. Copying a protected program on an ROM chip is a violation, Sloviter explained, for otherwise there would open "an unlimited loophole" in the Copyright Act. That ruling is "very, very important," says Chicago lawyer Thomas C. Elliott Jr., who worked for Williams on the case. He sees it encouraging other videogame developers to copyright programs encoded on their ROM chips as well as their sound and light displays. And that, in turn, should mean it is more likely that when arcade players take to the battlements, they are the real things and not mere copies.

But because the Philadelphia ruling specifically rejects a 1979 holding of a federal trial court in Chicago in a case unrelated to videogames, the impact is even broader. The Chicago court had said that chips that copy chips are not copyright violations. Now that a higher court has turned down that argument, copyrights should play a bigger role in home computers and a whole variety of other electronic gear.