Cable television's blessings have been few, and most of those mixed, but it can claim one great idea: C-SPAN, the Cable Satellite Public Affairs Network, which tonight celebrates its 10th anniversary with a three-hour retrospective. Available to only 3.5 million wired households when it began transmitting the proceedings of the House of Representatives on March 12, 1979, C-SPAN can now be seen in 43 million homes. On June 2, 1986, the Senate finally bit the bullet and turned the cameras on itself, and a second channel, C-SPAN II, was born. Once a novelty, then a kind of cult item, C-SPAN has become a seemingly indispensable feature of America's electronic landscape. If C-SPAN's combined regular viewership remains relatively small, it is also passionately loyal. In tonight's program, at 8 on C-SPAN, a Texas teacher recalls how he was compelled to quit his job and run for Congress because what he had seen on C-SPAN inspired him. Or maybe he just deduced that those jokers in Washington were in obvious need of his help. Bud Harris, a viewer in Cherry Hill, N.J., became outraged in 1982 when his local cable system (owned by The New York Times) dropped C-SPAN from its roster. The network had switched from sharing space on a satellite with another channel to a bird all its own, and the cable system, perhaps more in confusion than negligence, let it slip away. Harris founded Friends of C-SPAN and got the channel reinstated. Any cable system of moderate capacity or larger that doesn't include the two C-SPAN channels is guilty of civic malfeasance -- and poor public relations, since C-SPAN is the best image booster grubby old cable TV has ever had. It fosters the illusion that cable operators care about something other than making lots and lots of money. Tonight's C-SPAN retrospective is part of its celebration of (try to contain your enthusiasm) National Cable Month. On some systems, the two C-SPANs are relegated to the outer limits of the spectrum. In Arlington, for instance, where the highest channel number is 55, C-SPAN I and II come in on 52 and 53. The system reserves the better channels for those that produce revenue for the owners. But C-Spanners locate the channels wherever they are, and do more than watch faithfully. They participate, mainly by opining away on the network's frequent call-in shows. Often these are hosted by Brian Lamb, C-SPAN chairman and chief executive officer and last year's recipient of the Sol Taishoff Award for Excellence in Broadcast Journalism. On tonight's program, Lamb recalls how the idea for C-SPAN was set in motion in 1977 with a mere $25,000 investment from the cable industry. "It's basically talking-head television," Lamb concedes, but there are millions of listening heads out there taking it all in. Other familiar C-SPAN faces seen reminiscing include political editor Carl Rutan, vice president Susan Swain and producer-director Carrie Collins, who knew C-SPAN had arrived when she noticed that "the vast majority of reporters" covering the 1984 political conventions were watching C-SPAN's gavel-to-gavel service. If there are downsides to the C-SPAN story, one is that the traditional networks have used its existence, and that of Cable News Network, as excuses to abridge radically their own coverage of conventions and other political rituals. Cable still has less than 60 percent penetration of the country, so the network cutbacks have been at best premature. But most of the dire consequences predicted by those who opposed House and Senate TV coverage have failed to materialize. Do the members preen and posture before the cameras? No more, apparently, than they did before the cameras were there. They may dress better and have their hair cut more often. This is no threat to democracy. Some, of course, have taken to television better than others, as clips make clear on tonight's look-back. Sen. John Glenn (D-Ohio) joshed about makeup and red ties during the first day of televised proceedings; then-Sen. Howard Baker (R-Tenn.) had first introduced a resolution permitting cameras five full years earlier, in 1981, and that was two years after the House began telecasts. In other clips, Rep. Jim Wright (D-Tex.) offers a flamboyant recitation from "Gunga Din." Rep. Silvio Conte (R-Mass.) makes a certain angry gesture with his arm that has become one of the most replayed C-SPAN moments. In an excerpt from one of its daylong "Day in the Life" features, Rep. Robert Michel (R-Ill.) sings along with the "Hallelujah" chorus on his car radio. Meanwhile, back on the House floor, the whole body joins in a hearty chorus of "Happy Birthday" for Speaker Tip O'Neill, who was subsequently involved in a big brouhaha about control of the cameras. Rep. Robert Walker (R-Pa.) had been displeased to learn that while he rattled on during "special orders" at the end of the day, O'Neill had ordered that cameras pan the House chamber, revealing it to be virtually empty. Rep. Newt Gingrich (R-Ga.) joined in the roasting of the speaker. O'Neill was denounced but the panning continues to this day, a kind of visual memorial. Members of the raucous right sometimes seem to dominate C-SPAN, whether from the floor or on the talk shows. The TV stardom of Gingrich may have helped boost him into his newly won position as minority whip. Traditional whines about the media being liberally biased can hardly be aimed at C-SPAN; indeed, on tonight's show, sound bites from conservatives seem to outnumber those from the left and near-left. Ronald Reagan, the President Who Was Television, appeared many times on C-SPAN's "Close Up" series, during which Reagan answered questions from high school students. As a clip shows, Reagan was a viewer, too; he phoned in during a follow-up "Close Up" to clarify a point he'd made in a previous appearance. Only about half of tonight's special program was available for preview because the other half will be live. Former congressman Lionel Van Deerlin, present at the creation of C-SPAN and active in communications issues during his tenure, will be Lamb's guest during phone-in portions to talk about C-SPAN's first decade. The anniversary show will be followed by a typically ambitious C-SPAN project. On the eve of a potentially divisive mayoral election in Chicago, C-SPAN's cameras will cover a joint radio show by two Chicago stations -- one whose primary audience is black, the other whose primary audience is white -- as they open phone lines for listener comment. Part of what C-SPAN has accomplished is to make national events local and local events national. Its book about itself and its constituency was called "America's Town Hall," and C-SPAN has come closer to earning that title than any other communications entity. It also helps fulfill Marshall McLuhan's prophecy of the planet becoming a "global village" electronically linked. C-SPAN does an outstanding, exemplary, no-nonsense job, yet seems constantly to be undergoing improvement. It could also be said that C-SPAN has to some degree redefined citizenship; there's tele-citizenship (telezenship?) now. Government is less remote, less jeerable, more human to those who watch regularly. Laws that open previously closed doors to public scrutiny are called sunshine laws; in bringing Americans and their government closer together -- literally within arm's reach -- C-SPAN is ultimate sunshine.