Fifty years ago, viewers fell in love with “Lucy.” A few decades later, they watched “Mary Tyler Moore” make it after all.

But these days, there are few heirs to Lucille Ball’s or Mary Tyler Moore’s comedic throne.

If the half-hour sitcom is on life support, then the female-led half-hour sitcom has been given its last rites. Women aren’t the centerpiece of many laffers now, even as the nets continue to gravitate toward more femme-centric one-hour series.

At CBS, men dominate the net’s Monday night lineup — and the net’s one female-led comedy, “The New Adventures of Old Christine” (with Julia Louis-Dreyfus), was picked up for only 13 episodes and relegated to midseason.

Meanwhile, at NBC, “Comedy Night Done Right” means just one female-led comedy: the Tina Fey starrer “30 Rock.” And until recently, Fox (“The War at Home”) and ABC (“According to Jim,” “George Lopez”) were mostly testosterone fests.

The pendulum is starting to swing back, ever so slightly: TBS did well with one of its new comedies, “My Boys,” starring Jordana Spiro. And besides Fey and Louis-Dreyfus, ABC and Fox will attempt a handful of new shows led by women: “Sam I Am” (led by Christina Applegate) and “The Return of Jezebel James” (Parker Posey and Lauren Ambrose), respectively.

But there’s still a long way to go.

NBC casting chief Marc Hirschfeld notes that the entire comedy field is challenged, leading not only to a dearth of topline female sitcom roles, but to a dearth of sitcom roles, period.

“There just are not that many opportunities because the right comedies haven’t come out,” he says. “I’ve been lobbying the last couple of years to bring back a strong female-centered show to NBC.”

And indeed the networks are still trying to develop sitcoms, including many with a female bent.

“People are taking shots — for example, ‘Fugly,’ which CBS did (as a pilot) with Jenna Elfman,” Hirschfeld says. “And we are looking. I’d love to break that next big female sitcom star.”

“Everybody Hates Chris” star Tachina Arnold quips that fewer female lead roles better her chance of an Emmy nom — but then adds on a more serious note that she counts herself lucky to have secured one of the few leading roles out there.

“My thespian side feels very fortunate to be working, and to be on a show that’s good,” she says. “There are a lot of actors out of work right now. It’s unfortunate to see your peers not working, but that’s the nature of the business. I personally don’t want to see sitcoms go away.”

So where did all of the roles go? For one thing, family sitcoms went away, “Chris” being one notable exception. Family laffers could reliably employ men, women and kids to make up a fictional nuclear family.

Also, the nets spent much of the early part of the decade chasing down those elusive young men (particularly with procedural dramas). Young men, the conventional wisdom goes, will not watch female-

centered sitcoms. But young women will tolerate laffers starring dudes. Hence the decision to stick with guys; men, after all, still dominate the ranks of sitcom writers and producers anyway.

Fox casting chief Marcia Shulman has another theory: Actresses these days are too afraid to appear too slapsticky.

“Women in this business are very fearful right now, with the emphasis on beauty and looking as young as possible,” she says. “Women are afraid to make fun of themselves. So they avoid roles that require them to give that big-funny, no-holds-barred performance.”

Shulman also cites the modern backlash to feminism, which originally gave rise in the 1970s to the spate of female-driven shows like “Maude.”

Then, of course, there’s the obvious answer: Female-centered comedy didn’t disappear, only half-hour female-centered comedies did. They’re still thriving on the hourlong side.

As a matter of fact, if it weren’t for hourlong comedic dramas, Emmy would barely have enough candidates for the outstanding actress in a comedy category.

But these days the category is bursting at the seams with hourlong contenders (purists, who argue that hourlongs shouldn’t be allowed to compete in the comedy category, be damned): the “Desperate Housewives” women. “Ugly Betty’s” America Ferrera. “Weeds” star Mary Louise-Parker. “Men in Trees” lead Anne Heche. And others.

“Ten years ago, ‘Ugly Betty’ would have been a multicamera half-hour comedy with America Ferrera in the lead,” Hirschfeld says. “Shows like ‘Gilmore Girls’ or ‘Ugly Betty’ or even ‘Men in Trees,’ that’s where the comedic female lead has morphed into.”

Even “Friends” star Courteney Cox wound up in an hourlong, “Dirt,” for her follow-up act, he adds.

“I don’t think there’s a lack of strong, comedic females who could star on their own show,” he says. “Megan Mullally is still out there, Debra Messing is still out there. I don’t think it’s impossible. ’30 Rock,’ ‘Scrubs’ and ‘The Office’ all do a great job in creating characters that actors can sink their teeth into.”

Adds Shulman: “We’ve been working really hard to try and find that big, female comedic voice.”