''There is no doubt the big one is coming,'' the narrator says almost cheerfully. San Bernardino, with houses built on the San Andreas fault, will be particularly hard-hit. On then to California, and a story from Los Angeles magazine: ''Living on the Fault Line.'' Everyone seems to agree that a large piece of Southern California will soon fall down in rubble. There is a suggestion he's leading a very lush life.

Is he serious? ''Fast Copy'' seems skeptical. Wilson had some television flops and, apparently, personal problems as well. Wilson, who played opposite Redd Foxx in ''Sanford and Son.'' Then Mr. ''Occasionally, there is the story of a star performer who's fallen and made it to the top again.'' ''In more than three decades on the television beat, I've seen them come and go,'' Mr. The first story - ''Demond Wilson: Act of Faith?'' - is from TV Guide and is introduced by the magazine's editorial director, Merrill Panitt. Each story is introduced by an editor of the magazine in which it appeared.

The episode tonight, the fourth time out for ''Fast Copy'' this season, presents five stories, all of which originally appeared in magazines. If ''Fast Copy,'' without star reporters, can do a story about the possibility of San Bernardino, Calif., succumbing to an earthquake, can it also do a story about arms control, say, or Nicaragua? Does it matter? No, not on the stories we see tonight, but we are getting into a shiny new area. A narrator takes the place of the reporter. ''Fast Copy,'' though, pushes a step further. The NBC program is punchy, but not that punchy, although the premise is the same: Get in and get out of a story as quickly as possible, with a modicum of entertainment in between. Say now that ''Fast Copy'' doesn't have the high style of CBS's ''West 57th,'' which is high on video, too. Meanwhile, even if it's not trying to, ''Fast Copy'' is slyly raising a question: Does television need reporters? The NBC program, on Channel 4 at 10 o'clock tonight, relies on video. In other words, it's ''infotainment,'' or popcorn news, and as such, it's not bad at all. ''FAST COPY'' is an entertainment program that looks like a news program, or maybe it's the other way around.

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