With one nod of the feather on her astonishing chapeau as she swept into the "FYI" studio last season, Colleen Dewhurst grabbed the role of Murphy Brown's steely-babe mother, Avery, and made it hers for life: Dewhurst as Mom to Candice Bergen's Murphy is casting made in TV heaven.

With one twist of the pool cue she wielded (with cut-throat cordiality) on a visit to her steely-babe daughter a few episodes ago, Dewhurst retained championship possession of one of the hottest guest roles available for older actors today -- that of TV parent to a character in an ongoing series.

If "Murder, She Wrote" is the Lawrence Welk Retirement Home for veteran actors who used to do a booming TV business in the 1960s, trendy '90s shows like "Murphy Brown" and "L.A. Law" and "thirtysomething" have now become the hip nightclub spots in which to gain a whole new yuppie fan club among post-modern viewers.

They're the ones who never knew, say, that Alan King is not just a loud, sour, comic who appears on the "Tonight" show from time to time. Turns out King also has it in him to play a surprisingly dignified, vulnerable, lifelike widower who dates Michael Steadman's mom and holds Michael's son at the baby's bris on "thirtysomething." And in doing so, he wowed the home audience so well that producers Marshall Herskovitz and Ed Zwick are now looking at scenarios in which King might return.

"The casting choice," says Herskovitz, "came totally from the gut. Now everybody loves him."

Put it this way: Eddie Albert's golden reputation, buffed to a high kitsch twinkle by his 120-year run as Oliver Wendell Douglas on "Green Acres," got a whole new glow after he stopped by as Elliot Weston's father on "thirtysomething."

Now we've got Rose Marie as Frank's mother on "Murphy Brown," a quarter-century after playing Sally Rogers on "The Dick Van Dyke Show."

And, come to think of it, we've also got Darren McGavin as Murphy's father, after years of being, well, Darren McGavin.

From the big-screen roster, we've got Frances Sternhagen as Cliffie's ma on "Cheers" and Vincent Gardenia as Roxanne's pa on "L.A. Law."

From the high-art stage, Estelle Parsons gives a great low-down performance as Roseanne Connor's mother on "Roseanne."

From the living-legend roster, Sylvia Sidney showed up as the Steadman grandma on "thirtysomething."

The trend toward inspired casting in the category of cameo parent may well be said to have begun a few years earlier, with "St. Elsewhere" and the genius pairing of Steve Allen and Jayne Meadows as Victor Ehrlich's parents.

But nowhere is the casting so consistently on the money as with the elders on "thirtysomething," where Barbara Barrie plays Michael's mother, George Coe plays Hope's dad (in a bit of cross-network dressing, he also dated Murphy Brown's mother recently), and Phyllis Newman plays mother to Melissa Steadman.

Gut instincts have yet to seize on Steve Lawrence and Eydie Gorme as somebody's parents. Anybody's. But there's still hope. On today's TV, cameo parents are hits with TV-watching kids.