In the campaign to win what generally is considered the most prized cable television franchise in the Washington area, Roscoe Nix plays a key role.

Nix, head of the Montgomery County branch of the NAACP, has been approached by virtually all of the 20 firms seeking the cable franchise for the county, each anxious to explain to his organization what its proposal is all about.

"They give us their program and then ask us what we would like to see them do," says Nix. "They have not asked for endorsements, but what they will say is, 'look, we've touched base with all these people.' ".

While aggressive marketing and sophisticated public relations are nothing new in the cable TV franchise battles that have gone on in the Washington area in recent years, the special circumstances of the Montgomery County competition have made companies like Times Mirror and Warner-Amex develop and refine their techniques even further.

Steeped in good government tradition and anxious to prevent even the hint of a scandal, Montgomery County officials have instituted a number of strict regulations prohibiting any county decision-makers from even discussing cable television with the representatives of cable firms, except at public meetings

As a result, community and civic groups such as the NAACP have come to play a key role in the selection process. If companies cannot approach the people who actually make the decisions, they can at least talk to the people who have some influence over those who make the decisions.

As part of the strategy, for example, Times Mirror has begun publication of a slick monthly newsletter called Cable-Gram, complete with photographs and stories about Times Mirror. The newsletter is mailed out to citizen associations and civic groups.

Last week, a score of civic leaders, prominent county Democrats and some journalists received invitations to a special cable television screening of the Sugar Ray Leonard-Thomas Hearns fight, courtesy of Warner-Amex.

Contacts with community groups are made under the general heading of "community ascertainment" -- which is cable TV jargon for "give the people what they want."

To tailor their applications specifically to the local needs, the firms spend a good deal of their time interviewing the heads of the local United Way chapter, public libraries, public schools, and churches, asking what they want to see in a cable system.

While cable firm representatives state emphatically that they do not seek endorsements during these interviews, "community ascertainment" is seen as one way for a cable firm to get its name known out in the community.

"Community ascertainment is a form of public relations," says John Hansman, the county's cable TV project manager.

With the stakes in the Montgomery competition so high -- the winner virtually will be guaranteed a monopoly over cable television for the next 15 years with profits conservatively estimated at over $20 million each year -- the cable companies have enlisted a wide range of prominent county lawyers and politicians. The chairman of the county Democratic Committee, Stanton J. Gildenhorn, for example, represents one firm, Tribune/Rogers Cable Systems of Montgomery County.

So far, officials who will have some say in the selection process assiduously have avoided the swarm of cable firm representatives.

In July, for instance, a Gilchrist aide returned two checks to campaign contributors, because both supporters had interests in cable companies.

Already, council-passed laws require cable lobbyists to register and in the future the firms will have to disclose all of their lobbying and public relations expenses .

Today, when the County Council finalizes the county's proposals for a cable system -- which formally opens the application process -- the council members are expected to tack on a provision prohibiting any of the competing firms from contributing to a political campaign for three years after the franchise is awarded. The winning firm would be prohibited from campaign contributions for the life of the franchise.

"Some people say that we've bent over backwards and gone too far" with the lobbying restrictions, said council president Ruth Spector. "But we've waited long enough in the county to see other jurisdictions get into trouble."