Wednesday’s third and final debate between presidential contenders John McCain and Barack Obama drew a significant audience on the multiple broadcast and cable outlets that carried it, although the crowd was smaller than that for last week’s chat.

Nielsen Media Research estimates that coverage of the debate Wednesday from 9 to 10:30 p.m. ET on ABC, CBS, NBC, Univision, BBC-America, CNBS, CNN, Fox News Channel, MSNBC and MUN2 combined to draw 56.52 million viewers — down from the 63.23 million for last Tuesday’s debate but up from the first get-together on a Friday three weeks ago (52.42 million).

Last week’s debate was the most-watched presidential debate in 16 years. It was, however, topped by the only vice presidential debate of this season between Joe Biden and Sarah Palin, which averaged a whopping 69.9 million viewers.

Baltimore, Washington DC and St. Louis had the highest ratings Wednesday, and New Orleans, Los Angeles and San Antonio had the lowest.

Nielsen didn’t issue national debate ratings for the broadcast nets, but Fox News (9.07 million) led cable by drawing slightly more viewers than CNN (8.93 million), while MSNBC averaged 3.72 million. CNN, though, held a comfortable edge in the key news demo of adults 25-54, with its 3.5 rating/7 share nearly as big as Fox News (2.4/5) and MSNBC (1.2/3) combined.

In the post-debate window from 10:30-11 p.m. ET, for which broadcast ratings were released by Nielsen, NBC led the way with 9.09 million viewers, followed by ABC (8.86 million), CNN (7.80 million), Fox News (7.39 million), CBS (7.19 million) and MSNBC (3.60 million).

Likely contributing to lower numbers this time around was the fact that Fox, which had aired the previous debates, broadcast the baseball playoff contest between the Philadelphia Phillies and Los Angeles Dodgers. That game averaged 8.03 million viewers (and a 2.6 rating/7 share among adults 18-49) — on par with the previous mediocre results for the series.

In Wednesday’s opening hour, NBC’s “Knight Rider” (2.3 rating/6 share in 18-49, 7.47 million viewers overall) edged past the demo deliveries of Fox’s baseball and CBS’ comedy duo of “The New Adventures of Old Christine” (2.2/6 in 18-49, 7.61 million viewers overall) and “Gary Unmarried” (2.3/6 in 18-49, 7.53 million viewers overall).

Also, ABC’s “Pushing Daisies” (1.9/5 in 18-49, 6.11 million viewers overall) continues to perform sluggishly, while CW got decent numbers for its midseason clip show of “America’s Next Top Model” (1.5/4 in 18-49, 3.21 million viewers overall).