Cable industry leader Comcast (NASDAQ:CMCSA) is checking in with solid quarterly numbers, but like most of the rest of the market, it seems to fear gloomier times ahead.

For the just-completed third quarter quarter, Comcast earned $771 million, or $0.26 a share, versus $560 million, or $0.18 a share, in Q3 2007. Revenue grew 9.9% to $8.55 billion in the same period.

Echoing a host of companies and industries, from oilfield services leader Schlumberger (NYSE:SLB) to aluminum manufacturer Alcoa (NYSE:AA), Comcast CEO Brian Roberts indicated during his conference call that a slowing economy may make future quarters' results less solid. Fewer customers appear willing to sign on for telephone service, the newest addition to the company's triple play, with more and more subscribers opting instead for other companies' wireless service. In the September quarter, the company added 483,000 telephone customers, down 29% from a year ago.

At the same time, Roberts acknowledged that Comcast is experiencing increased competition from telephone companies Verizon (NYSE:VZ) and AT&T (NYSE:T). Both have continued to add service capability within Comcast's franchise areas.

Comcast, with more 24 million cable customers, has grown steadily throughout this decade. It also serves roughly 14.7 million high-speed data customers and 6.1 million voice subscribers. The company continues to roll out faster Internet services, along with a new slower offering for cost-conscious customers. Indeed, the company's concern about the future relates to many customers' unwillingness to pay up for premium services.

The second- and third-largest cable providers, Time Warner Cable (NYSE:TWC), and Cablevision (NYSE:CVC), will report their earnings next week. Each is expected to exceed last year's earnings per share; Cablevision may even move from a year-ago loss to a profit.

Comcast shares are down a third from their 52-week high. As much as I admire Comcast and its management, I'd warn Fools to avoid this stock until the economy calms down.

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