Fox’s “American Idol” continues to grow — in more ways than one — but CBS has come up with a better plan than anybody else to combat it on Tuesday nights: Call in the military.

As the music competition skein set more records on Tuesday, the Eye countered nicely with its military-set drama duo of “NCIS” and “The Unit.” Latter held up well in its second outing, keeping CBS in runner-up position on a night Fox has come to dominate.

“American Idol,” meanwhile, delivered its best numbers ever for a performance show (13.7 rating/33 share in adults 18-49, 32.77 million viewers overall). It was up 19% in 18-49 vs. the same night a year ago (11.5/30) and is up 11% for all nights through Tuesday.

The two-hour 18-49 average on Tuesday for “Idol” was just below what the Academy Awards netted for ABC earlier this month (13.9/33).

Fox’s rivals have had to grin and bear it, as “Idol” has not only expanded its ratings this season but also its airtime.

Through Tuesday night, Fox had devoted a whopping 1,569 minutes to “Idol” this season — an increase of 38% (or 7½ hours) vs. the 1,141 minutes of a year ago.

But who can blame the net for riding a hot horse? The show comes on — doesn’t matter if it’s opposite the Olympics, “Survivor” or whatever — and auds gobble it up.

Much of that expansion has come on Tuesday, and at the expense of Fox’s highest-rated scripted skein, “House.” Next week will mark the sixth time “Idol” has aired a two-hour edition on Tuesday this season — compared with just once a year ago — so fans of the medical mystery often are left waiting weeks for an episode.

Net that has best counterprogrammed “Idol” is CBS, whose third-year Mark Harmon starrer “NCIS” (4.4/11, 17.55m) matched its series high in 18-49 and 25-54 (6.1/14) with an episode in which the son of a military officer held a classroom of students hostage.

That led in to “The Unit” (4.9/11 in 18-49, 18.07m), which declined a mere 4% in 18-49 vs. its strong preem of one week earlier (5.1/12) despite facing “Idol” instead of “House.”

The Dennis Haysbert-fronted drama again had its best showing in key demos among adults 25-54, with a 14 share in both men and women.

Also Tuesday, the news wasn’t good for ABC’s critically admired “Sons & Daughters.” Back-to-back original episodes from 9 to 10 averaged a 1.9/4 in 18-49 and 5.15 million viewers overall, a 42% decline in the demo vs. last week, when it faced “House” instead of “Idol.”

NBC’s competing comedy “Scrubs” (2.7/6 in 18-49, 5.80m for an original seg at 9) moved ahead of “Sons,” which placed fourth in key demos, although “Sons” was in line with its lead-in, “According to Jim” (1.9/5 in 18-49, 5.62m).