DRAFTING a cable television franchise has become an extraordinary intellectual challenge. It's getting steadily harder because the technology is accelerating. City and county governments find themselves creating monopolies of great value to provide services that keep outgrowng the lawyers' definitions.

All three of the big suburban counties here -- Prince George's Fairfax and Montgomery -- are now in the process of picking the companies that will get their franchises. To county officials, it's unnerving to realize that the possibilities of cable television are expanding literally from month to month. The rapidly multiplying channels are capable of operating in both directions to provide catalog shopping, protection of homes and information ranging from stock market quotations to the times planes arrive at Dulles. One great preoccupation of the local governments is to avoid freezing the level of service at its present stage. The aim is to keep pressure on the cable systems to add new services as the engineers invent them.

A related issue, nationwide, is whether local governments should be allowed to recapture some of the very great financial value of these franchises. In areas as large as the Washington suburban counties, they are arguably worth hundreds of millions of dollars. Should the cable companies be required to bid competitively for the franchises?

National policy discouraged that idea. The principle has been that the revenues should go into technological improvement and expanded service. There's a fear that hard-press cities might extract high prices for the initial operating rights, at the expense of the quality of subsequent service. But in view of the enormous commercial values now attached to the monopolies being created here, perhaps those aims -- good service and more tax revenue -- and not entirely contradictory. It's time for the FCC to reconsider the possibilities.

The prospect of high profitability has already attracted a number of local political figures into the scramble for franchises in this area. Promoters sometimes claim that a local company will serve the community best. But as the cable television industry comes increasingly to be dominated by a small number of big companies operating nationwide, the local connection has become an expensive sham. Montgomery County has set a useful example of telling prospective applicants that adding local politicans to their boards will not be counted in their favor.

When the FCC gave out the early radio and television licenses, it knew fairly precisely what it was offering. Now it has devolved the cable decisions onto local governments, each of which is likely to hand out its franchises only once. Worse, none of these local governments can know exactly what that new wire is capable of carrying -- a family of programs and services, certainly, but a family that seems to be growing endlessly. All three counties are moving toward decisions slowly, sensibly and very cautiously.