HOLLYWOOD — “American Idol,” “Desperate Housewives” and “CSI” are the shows racking up the biggest ratings this season, but for every one of these megahits, there’s a lesser-heralded skein quietly getting the job done.

Here’s a look at the program at each network that rates among this season’s unsung heroes:

“Cops” (Fox) — Saturday’s are a drag for the other nets but not Fox, which has relied on this unscripted law enforcement series to kick off the night for 17 seasons. Paired with the similarly ageless “America’s Most Wanted,” Fox again led Saturday this season in all key ratings categories.

In fact, “Cops” (2.7 rating/9 share in adults 18-49 for its hour, according to Nielsen) has maintained its average for a couple of years now while the hodge-podge lineups at ABC, CBS and NBC have declined.

“Las Vegas” (NBC) — In an hour that includes tough competish like “Monday Night Football,” “Everybody Loves Raymond” and “24,” this light drama is perfect counterprogramming — and a solid ratings performer.

“Las Vegas” (4.4 rating in 18-49) is down 10% from its strong rookie season, but that’s actually impressive since lead-in “Fear Factor” has tumbled by a big 27% year-to-year. Also “Vegas” didn’t have to face a hit drama like “24” a year ago.

Since “Football” ended, “Las Vegas” has consistently led its timeslot in adults 18-34.

“NCIS” (CBS) — This not-quite-a “JAG”-spinoff has blossomed in its second season, regularly finishing second to Fox’s “American Idol” in Tuesday’s leadoff hour (3.1 rating in adults 18-49) and is up 15% year-to-year.

Growth here is not surprising for regular viewers of the show that has probably improved more this year than any other sophomore skein. More laughs than many sitcoms and more realistic workplace dialogue than heavier cop dramas, “NCIS” sets just the right tone for an 8 o’clock drama.

“One on One” (UPN) — Although ratings for its Monday comedy block are down across the board, this vet continues to plug along despite airing in its third different timeslot in as many seasons.

“Girlfriends” remains the net’s 9 o’clock comedy anchor, but this father-daughter laffer averages a solid 1.3 rating kicking off Monday night — up from its average on Tuesday last year.

“Steve Harvey’s Big Time Challenge” (WB) — Perennially unheralded Friday Frog laffer “Reba” would again be a good choice here, but this year’s nod goes to a comedy/variety show that has consistently been asked to plug the toughest hours on the net’s sked (now Sunday at 9).

Its urban and male appeal doesn’t make it a natural mesh with the rest of the WB’s lineup, but its versatility (30 or 60 minutes) makes it tempting for the Frog to want to keep this utility player on its bench.

“20/20” (ABC) — It would have been easy to write off this vet newsmag after Barbara Walters ankled last year, but it has held up well in the ratings (2.8 in 18-49) even if the rest of the net’s Friday lineup spiraled downward.

Give credit to co-anchors/reporters Mark Stossel and Elizabeth Vargas and producers for consistently delivering the most watchable news hour on the primetime sked — heavy on investigative and human interest reports at a time when many mags are bogged down on crime stories.

Since football season ended (and “60 Minutes” no longer enjoys big lead-ins), “20/20” has often stood as the week’s top newsmag in key demos.