With just nine days left until Montgomery County Executive Charles W. Gilchrist is scheduled to select a cable television firm to wire the county, the competitors have launched a costly last-chance advertising blitz in local newspapers hoping to sway Gilchrist's decision.

The three top-ranked cable firms and a fourth, long-shot firm with some key community group endorsements, have taken out full-page advertisements in the Montgomery Journal, the Montgomery Sentinel, and the Maryland Weekly section of the Washington Post.

The advertising effort is a costly one -- the full-page ads in the Post cost about $4,900 each -- although firm officials won't say exactly how much they're spending. But most are blunt about the target.

"The person we're trying to influence is the county executive, who will be making the decision," said Alan Dessoff, a spokesman for First County Cable, a firm partly owned by sports entrepreneur Abe Pollin.

"We're interested in reaching the decision-makers," agreed Jane Lampman of the third-ranked firm, Viacom Cablevision of Maryland.

One reason the cable companies decided to launch their ad campaigns was that county officials are prohibited by county statute from discussing cable television or the process with industry representatives. The firms were not allowed to participate when Gilchrist briefly reopened the public record, despite a year-long public hearing process, to allow additional remarks from community groups who felt they didn't have enough time to comment. About 100 letters came in from the public, most of them apparently generated by the cable firms or their supporters.

Despite being the subject of all this unwanted attention, the decision-maker, Gilchrist, is oblivious, an aide said. "It's very flattering," said his special assistant Edmond F. Rovner. "I had no idea this was all aimed at him." Gilchrist has promised a final selection by Oct. 15.

In the ads, each firm touts its particular qualifications. Tribune-United Cable, recommended for selection by the county's cable television project manager John Hansman, has taken out ads this week in the Journal and the Post, reminding Gilchrist that it was the first pick. The Post ad is headlined "It All Comes Down To This . . . " and lists what the firm, and Hansman, consider its strong points -- its promise to wire 100 percent of the county and its guarantee of the lowest entertainment rate.

Tribune-United's ad in the Journal is headlined "Montgomery County Deserves the Best . . . " Included are favorable quotations from the project manager's report and from the report of an advisory committee.

"We have been very low-key, and we just wanted to let people know we're still there," said Tribune-United's Jane Simon, who described the ad campaign as "subtle." "This is a very subtle county," she said.

Montgomery Cable Communications, Inc./Times Mirror Cable Television -- which Hansman recommended as his second choice despite ranking the firm first according to predetermined criteria -- this week began the last of its series of three newspaper ads emphasizing different themes. This week's ads, in the Journal and Sentinel, stress the firm's 35 percent local ownership, which spokesman Cory DeGeus said means greater accountability. The ad features the photographs of 38 active Montgomery residents and part-owners, above the heading "Cable That Cares. From People Who Care."