Montgomery County's citizen advisory committee on cable television said last night the Tribune-United firm tops a group of closely ranked applicants and should be granted the county's lucrative cable franchise.

That decision represents the first time one of the county's three top franchise selection advisers has picked a single firm to recommend for the franchise.

The 15-member citizens committee was selected and approved by County Executive Charles W. Gilchrist and the County Council in 1980 and was charged with representing community interests in ranking the eight firms competing for the franchise. Its findings will be considered when Gilchrist makes a final choice in late August; he is also to take into account findings of a consultant and the county's cable project manager.

A draft of the citizens committee report said the Tribune-United cable firm should be "selected by the county for negotiation of a strong and enforceable franchise agreement."

The panel cited the firm's commitment to wire the entire county, and its proposed low monthly rates for subscribers. Tribune-United is a joint venture involving the Chicago-based firm that operates the Chicago Tribune.

Montgomery Cable Communications Inc./Times Mirror Cable Television, a joint venture involving a local firm whose board chairman is R. Robert Linowes, a prominent Montgomery lawyer, was rated second by the citizen panel; it is currently given top ranking by both the cable project manager and the consultant.

The citizens panel ranked Viacom Cablevision of Maryland Inc. third and First County Cable fourth.

John Hansman, the cable television project manager, is working on a final presentation for Gilchrist and has stated that Times Mirror is only one percentage point above Tribune-United and Viacom in a top group of three.

Carl Pilnick, the county's independent consultant, had an even larger top group, with Times-Mirror leading Tribune-United, Viacom, Tele-Mont Communications and First County.

Once Gilchrist has made a selection, the County Council must approve a 15-year franchise agreement contract with the winning firm. That process is expected to begin in September.