A leading national consulting firm has abruptly stopped advising Fairfax County on how to award its lucrative cable TV franchise, angrily charging that the county's "inexperienced staff" has developed a "seriously flawed" cable proposal.

The resignation of Malarkey, Taylor and Associates comes one week before the county Board of Supervisors is expected to approve guidelines for what type of cable system it should seek from the 24 cable television firms interested in doing business in the county.

That approval, already delayed several times, could be thrown in doubt again by Malarkey's departure, which the Washington firm itself called "extraordinary." County officials said yesterday that the resignation will not delay the scheduled awarding of a franchise, now expected next summer, two years later than originally planned.

The cable company that wins the franchise will have an exclusive right to provide cable television to one of the most lucrative markets in the country. A study this spring estimated the franchise to be worth as much as $260 million 15 years from now.

Because the stakes are so high, the county has been determined to fashion a franchise that will lead to a foolproof, watertight contract. County staff members have made many changes in a draft request that Malarkey submitted one year ago.

In a letter dated Oct. 9 and obtained yesterday by The Washington Post, Martin F. Malarkey said those changes could leave the county more, not less vulnerable to the kinds of problems that have recently troubled Arlington, Alexandria and other municipalities. Malarkey wrote that the county's form will discourage qualified applicants from bidding and increase the risk of "expensive and time-consuming lawsuits."

"Since we feel that the proposed RFP request for proposals is so seriously flawed, we believe that we have no alternative other than to resign our position as consultant to the county-- a role which, we feel constrained to emphasize, we have actually not been permitted to fulfill for the last year or so," Malarkey wrote.

County staff members were reluctant yesterday to discuss Malarkey's letter, which the Board of Supervisors had intended to discuss in an executive session at its meeting next week. Several supervisors defended the county's position yesterday and suggested that Malarkey, Taylor, which works for cable companies as well as counties and towns, was not as interested as Fairfax in community access to cable and similar issues.

"I don't think they liked all of our disclosure requirements," said Supervisor Audrey Moore. "Our changes made it more in the best interests of the people of the county, gave them more safeguards, and I had heard they were unhappy about that."

County staff members said they were mindful of problems other counties have encountered: companies not providing the local access to cable channels they promised, not having the financial capability to provide as many services as they promised or -- as in Alexandria -- deciding to sell their franchise to other firms that may not be bound by the original company's promises. In addition, Fairfax has attempted to limit the possibility of improper lobbying by influential citizens hired by wealthy cable firms to put pressure on the board.

Staff members said their request for proposals addressed issues of financial disclosure and community access more fully than Malarkey's original draft. They rejected Malarkey's charge that "the county was being led down such a perilous course by its inexperienced staff."

Gary Hurvitz, a vice president with Malarkey, said his firm does work for cable firms, although usually not in franchising deals. He said that involvement did not affect the firm's attitude toward Fairfax. "The fact is we're a hired gun with a particular expertise, and we represent the interests of those who have retained us," he said.

Hurvitz also said he had no objection to the county's insistence on extensive financial disclosure or emphasis on community access. He said the way the county was asking its questions, however, would lead to problems.

"Community involvement has to be tempered with expertise," Hurvitz said. "Otherwise you either end up reinventing the wheel, or you end up with what we have now -- a Christmas tree of proposals that obscures the important issues."

The Fairfax board will be asked Tuesday to hire another consultant to finish Malarkey's work -- evaluating the cable proposals, at a cost of $8,000 each.

Malarkey had a $50,000 contract with Fairfax and had received $41,600. Hurvitz said the firm would have had to renegotiate its contract, because of the delays, even if it had worked out its differences with the county.

Board Chairman John F. Herrity rejected Malarkey's criticism of county staff but said he agreed with the complaints about how long the process has taken. Herrity said he and two other board members "regularly . . . said the county is wasting time and costing taxpayers' money with incessant delays."