`CSI’s’ Marg Helgenberger in a comfortable niche

There’s a home for fortysomething actresses: It’s called TV.

Marg Helgenberger has thrived there for the last seven seasons on “CSI: Crime Scene Investigation,” in which she plays the Vegas forensic night cop, single mom and former exotic dancer Catherine Willows.

Long-term success has allowed Helgenberger to fit movies in on hiatus, such as “Mr. Brooks,” which opened Friday. But she knows where her bread is buttered.

“A lot of women watch TV,” she says. “Most movies that are financed are catering to an age range of teenage boys.”

So she seizes the smaller opportunities on the big screen. In “Mr. Brooks,” she’s plays the good woman standing by her man, played by Kevin Costner.

“I just wanted to make sure I’m in the pocket, that we appear to have a loving relationship,” Helgenberger says.

Did we mention that Costner is playing a Jekyll-and-Hyde serial killer? One can imagine the director yelling, “OK, Marg, do blissfully ignorant.” Helgenberger jokes that her “CSI” alter-ego would have nailed this guy. But in this alternate reality, she is “blinded by love” as her spouse continues his nocturnal hunting with his devil’s-advocate subconscious (portrayed by William Hurt).

Helgenberger has a pretty comfortable routine for an actress defying the industry’s age bias. Each year, she cranks out 20 or so episodes of “CSI,” finds a movie gig to keep her out there on the big screen and maybe squeezes in a Hawaii vacation with actor-husband Alan Rosenberg and son Hugh. Free time has been scarce since Rosenberg was elected Screen Actors Guild president in 2005. Asked to name the most pressing thespian labor issue, Helgenberger answers, “Protecting residuals. That’s an actor’s lifeblood.”

Helgenberger has collected a few residuals herself. She broke in on “Ryan’s Hope” after being spotted in a Northwestern University staging of “Taming of the Shrew”; earned an Emmy in 1990 on “China Beach”; and made a prime-time comeback with “CSI,” which premiered in October 2000.

As for “Mr. Brooks,” she and Costner are talking about a sequel. She says Costner has told her that the movie must make in the range of $40 million to $50 million “and we’ll be fine.”

The film grossed an estimated $10 million in its debut weekend.