Sens. Hillary Rodham Clinton and Barack Obama together will spend close to $5 million on TV ads in the closing week before the state's Democratic presidential primary Tuesday.

Philadelphia stations will take in more than $2.5 million of that total, including $445,000 spent on cable - an impressive 17 percent. Cable's average for the five weeks running up to the primary is even more impressive: 22 percent.

"Four years ago, I would have sung and danced on Broad Street for 10 percent," says Jim Gallagher, head of Comcast Spotlight, the cable giant's advertising division. "We're incredibly gratified."

Obama continues to outspend Clinton here by more than a 2-1 ratio. On Fox29, for example, he bought 30-second spots on every single Fox prime-time show for the week.

That's 15 programs, including House, Bones, Cops, America's Most Wanted, Are You Smarter Than a Fifth Grader?, The Simpsons, Family Guy and American Dad.

He bought three spots on powerhouse American Idol, at $22,500 a pop. Idol was Clinton's only prime-time buy. She has one spot.

The differential in Philadelphia is even higher in cable: Obama bought $378,000 (22 percent of his total buy) in the final week to Clinton's $68,000 (8 percent.)

Nationally, cable accounts for about 20 percent of political ads this election cycle, experts say, up sharply from the 2004 presidential campaign.

Then, candidates bought cable time "to an embarrassingly low extent," Gallagher says. "They didn't understand we were able to deliver such power for them."

Cable's advantage over broadcast TV is that it can target a specific geographic area, even a specific zip code, Gallagher says. Campaigns don't pay for voters they don't need to reach.

And with close to 55 channels into which commercials may be inserted, Comcast offers candidates numerous avenues to target a particular demographic, he says.

Along with news channels (CNN, Fox News, MSNBC), Clinton and Obama have bought spots on Lifetime, A&E, ESPN, BET, History Channel, Animal Planet, MTV, VH1, the Food Network and Sci Fi, according to Gallagher.

That strategy is not without risk, says Ira Teinowitz, Washington bureau chief of Adweek.

"It's one thing to buy CNN, but if you buy 10 other networks are you assured of getting people who are voting or are interested in voting?"

Or, as Evan Tracey of Campaign Media Analysis Group puts it: "Cable sells by the pint. Broadcast sells by the gallon."

There are other drawbacks. Not everyone has cable, especially satellite-dish owners. No sweat, Gallagher says. With 76 percent of the Philadelphia market wired for cable, "we're blessed."

Many share in the blessing. In the five-week run-up to the primary, Pennsylvania took in a total of more than $13 million in election-related TV spots. Philadelphia alone had $7.7 million, including $1.7 million for cable.

During that span, Obama spent $4.2 million and $1.4 million on broadcast and cable, respectively, for a total of $5.6 million. Clinton put out $1.8 million and $334,000 for a $2.1 million total.