One of the nation's leading cable television firms announced yesterday that it will not compete for Fairfax County's potentially lucrative cable franchise because the county is making unreasonable demands on all applicants.

The firm, Warner Amex Cable Communications Inc., had been expected to compete vigorously for the franchise because the company already provides cable service to Reston. But, in a letter to county Board Chairman John F. Herrity, the company complained that Fairfax is demanding an "enormous and burdensome" amount of information and is proposing to tax franchise profits too heavily.

The company's letter also raises the possibility that a decision on the right to serve Reston, which Warner claims but Fairfax intends to put out for bid, may have to come from the courts.

Warner's unexpected withdrawal is the second major jolt this fall to the county's cable process that, after three years, has been criticized for numerous delays. In October, the consulting firm that had been advising Fairfax angrily withdrew, charging that the county had developed an application form that would discourage qualified applicants and increase the possibility of lawsuits.

The stakes in the cable process are high, because the winner will have a monopoly that could be worth $260 million in 15 years, according to a study completed last spring. Because of the potential profits -- and because of allegations of corruption and influence peddling in other jurisdictions -- Fairfax officials have painstakingly attempted to fashion a corruption-proof application form.

Prince George's County recently fought the kind of battle Fairfax officials say they want to avoid. The council there ignored a citizen commission's recommendation and awarded a franchise to a company represented by a former county executive. The award was vetoed by County Executive Lawrence Hogan, whose veto was, in turn, overridden by the council.

Warner Amex charged yesterday that Fairfax has gone too far in its attempt to create safeguards, however. "Compliance with the shareholder information questions alone would entail extensive polling of shareholders and could also result in invasion of shareholders' rights of privacy," the company's letter said.