Skategate produced a ratings avalanche Wednesday beyond anyone’s expectations as CBS coverage of the skating prelims yielded the highest rating for any TV program since the final installment of “MASH.”CBS’ score with the Nielsen judges also represented the sixth-highest rating since 1960, when such records started being kept. The 48.5 rating, 64 share CBS delivered in primetime — all the more remarkable since the outcome was decided hours earlier — translates into 45.7 million homes, ranking behind only “MASH” (when the TV universewas considerably smaller) by that standard. The broadcast was seen by 78.8 million viewers on average and, in part, by a U.S. audience of more than 110 million. Only five programs have achieved a higher rating, led by “MASH” (60.2/77), which aired Feb. 28, 1983. The others are the “Who Shot J.R.?” episode of “Dallas” in 1980 (53.3/76), the final installment of “Roots” in 1977 (51.1/71) and two Super Bowls — in 1982 (49.1/73) and ’83 (48.6/69). CBS, which was able to orchestrate the tape-delayed coverage to sustain viewing throughout the night, peaked with a 53.4/70 share from 10-10:30 p.m., meaning more than half of all TV households were tuned in to the Games. Top Olympic ratings Wednesday’s tally insured that the current Olympics will be the highest-rated ever. In terms of the most direct comparison, numbers are running 44% ahead of results for the winter competition two years ago. Fox Broadcasting Co., whose youth-oriented audience has proven nearly Olympics-proof, experienced the smallest decline relative to its season-to-date levels, narrowly trailing ABC from 8-10 p.m. with “Beverly Hills, 90210″ and “Melrose Place.” Not wanting to waste original episodes, ABC threw in the towel, airing repeats of “Home Improvement” and “Grace Under Fire.” The four broadcast services combined for a 95 share of the viewing audience from 9-10 p.m. The number of households watching television, known as HUT levels , also soared. With coverage of Nancy Kerrigan skating for the gold medal to air tonight, CBS again figures to post huge numbers. In fact, the web’s all-time Nielsen record for a single week, established by its first full week of the Olympics, will almost certainly be bettered during the current frame. Boosted by the huge primetime lead-in, CBS’ “Late Show With David Letterman” scored its second-best numbers yet (12.6/33) in Nielsen overnight markets, finishing a tenth belowratings for the show’s Aug. 30 premiere.