CABLE COMES TO THE COUNTY****Time TBA. Channels 1-120.(1985). Science Fiction/Comedy. (R). Charles Gilchrist, David Scull and a cast of characters. A gang of county politicians signs up for a television franchise and never gets the picture. (See highlights for other reruns through other political channels).

LET'S ALL WELCOME Montgomery County viewers to America's favorite cable television game, "Bait and Switch," in which what you see is what you don't get from the company that's under contract to provide cable service. The news from Montgomery is this: the cable firm that promised the moon and a galaxy of brightly lit channels around the county has halted construction on the promised system indefinitely. The work stoppage has come only a week after officials of the cable firm Tribune-United Cable Co., revealed that they had asked the county for major contract concessions to stem serious financial losses that would result if the system were built as agreed to.

District of Columbia, please copy: Cable firms all over the country are pulling the wires out from under governments -- announcing that all previous bets are off, that they can't deliver as ordered. It was only the other day that the franchise award- winner in the District announced that it couldn't possibly do as it had told city hall in the first place. And the D.C. Council swallowed hard and said oh, well. Don't look now, or even in 1988 if you live in certain neighborhoods.

Who's to blame for all this thin air? Spread it around: 1) the cable bidders promise anything a government wants to hear -- fat fees for the local coffers, umpteen free channels and studios on every other corner for "public access" programs and more channels than the federal bureaucracy has -- and then pull back later; 2) the governments write up specifications for gold-plated systems at bargain-basement prices that hardly anyone really would use anyway.

But the District, Montgomery and any other government that has a signed contract with a cable firm should stick to its stipulations and demand delivery as ordered. Otherwise tomorrow's viewer will be looking not for cable but for a satellite dish -- or maybe a good book.