With no incumbent president or vice president running for president for the first time in decades, next year’s presidential race is already expected to be among the most contentious in years, setting records for political ad spending and money raised.

It’s also looking to be a hot one for the cable news networks, based on viewership for the first Democratic and Republican debates on MSNBC the past two weeks.

The Democratic debate, featuring eight candidates on April 26, averaged 2.26 million total viewers from 7 to 8:30 p.m., the cable news network’s best performance in that slot since March 19, 2003, the day the Iraq war began. MSNBC finished ahead of Fox News and CNN in the slot.

One week later, the Republican debate averaged 1.76 million total viewers from 8 to 9:30 p.m., just 400,000 behind usual cable news timeslot winner “The O’Reilly Factor.”

But what’s most interesting about the debates isn’t how they fared against the cable competition but how they compare with past presidential debates, affirming that viewer interest in this election is already higher than for the last one.

An October 2003 pre-primary presidential debate and post-debate coverage between the Democratic candidates averaged 1.61 million viewers on CNN in primetime. And MSNBC’s coverage of the three 2004 presidential debates between President George Bush and hopeful John Kerry peaked with 2.1 million total viewers, 160,000 fewer than tuned in for the Democratic debate.

This year’s numbers could grow bigger still, with debates set for CNN in June and Fox News Channel later this summer.

While some have moaned that the 2008 presidential campaigns kicked off too soon, there’s clearly a huge amount of interest in them. A big issue for all the candidates is the Iraq War, this year’s No. 1 news story, according to the Project for Excellence in Journalism.

But the candidates themselves are also getting lots of media attention, which may be spurring voters to tune into debates. The PEJ found that the 2008 presidential campaigns accounted for 13 percent of all TV, radio, newspaper and online news for the week ended May 2.

Too, the rearranged primary dates for several states this year may be fueling a desire to learn more about the candidates, as voters cast their ballots earlier than ever before.

Meanwhile, in other cable ratings for the week ended May 6:

Top five networks in primetime (18-49s): TNT, USA, FX, TBS, Spike

Top five networks in primetime (total viewers): TNT, USA, FX, Fox News, TBS

Top movie (18-49s): TBS’s “The Lord of the Rings: The Two Towers” (Sunday, 8 p.m.) 1.41 million

Top sporting event (total viewers): TNT’s “NBA Playoffs: Golden State-Dallas” (Thursday, 10:40 p.m.) 4.83 million

Shows making the top 10 among 18-34s, 18-49s and 25-54s: USA’s “WWE Entertainment” (Monday, 9 p.m. and 10 p.m.); TNT’s “NBA Playoffs: Mavericks/Warriors” (Thursday, 10:40 p.m.); TNT’s “NBA Playoffs: Spurs/Nuggets” (Monday, 10:33 p.m.); ESPN’s “NBA Playoffs: Warriors/Mavericks” (Tuesday, 9:55 p.m.); “TNT’s NBA Playoffs: Lakers/Suns” (Wednesday, 10:32 p.m.)

Show on the rise: TNT’s “NBA Playoffs: Golden State-Dallas,” Thursday 10:40 p.m. The game in which the top-seeded Mavericks got bounced was the second-highest-rated NBA game on broadcast or cable this season, drawing more than 3.7 million households and leading TNT to No. 1 in all the major demos in primetime.

Show on the decline: Discovery’s “Deadliest Catch,” Tuesday 9 p.m. The show about Alaskan crab fishermen fell 17 percent week to week in adults 18-49, from 2.16 million to a still-strong 1.797 million.