In the Pacific time zone, the network is positioning the program as sort of a national newscast for the West. Tonight, Elizabeth Vargas will anchor from Los Angeles with Bob Woodruff in San Francisco. "World News Tonight" launched a live West Coast edition on Jan. 5. The move was designed to attract viewers in the West with the promise of a fresh newscast after the three-hour time difference from New York. Yet so far, the West Coast edition and addition of Vargas and Woodruff as permanent co-hosts has not posed a formidable challenge to "NBC Nightly News with Brian Williams." Last week, the first full week of the refashioned ABC newscast, NBC led by 13 percent among both total viewers and in the key adults 25-54 demo.