OF MARYLAND LEGISLATORS fall asleep at the switch and fail to enact a cable franchising bill now before them, you can click off those extra- channel screens in Montgomery County indefinitely. Without the legislation--which would grant to localities in Maryland the same immunity from antitrust lawsuits already enjoyed by the state government in cable-franchising decisions--Montgomery's franchise decision could be delayed as much as two years.

That's the unwelcome but cautionary word from County Executive Charles Gilchrist, in the wake of a Supreme Court decision last Jan. 13 that complicated cable life for many localities across the country. Here, in a nutshell, is why: the court's decision makes localities liable for antitrust suits if they award exclusive cable franchises without state authority. Most localities in Maryland already have granted such franchises, assuming they were protected under the state's blanket of immunity. But Montgomery is just now wrapping up a long process aimed at coming up with a franchising recommendation in June, to be followed by the solicitation of bids.

Sponsors of the cable bill, SB 872, note that the measure is designed merely to reinstate what had been understood all along to be the authority of Maryland's home-rule governments to award franchises, establish rates and regulate service. The bill would not grant any new or extraordinary powers to governments. Nor is it intended to overturn any past decisions (for better or for worse) made by other localities.

But legislative time is short now, with three weeks to go before the General Assembly session ends. For the sake of an orderly transition to cable throughout Maryland in general and in Montgomery right now, the bill deserves priority consideration and a strong vote for enactment.