A certain female presidential candidate has driven Mary McDonnell to abuse an unsuspecting piece of silverware. Rather than use the fork to poke at her poached eggs, McDonnell — who knows from female leadership after three seasons as President Laura Roslin on Sci Fi Channel’s Battlestar Galactica — smacks it against the palm of her hand as if it were a bullwhip. ”Now, this is what the country is asking of Hillary Clinton: ‘Talk about your [decision-making] process in your vote to authorize to go to war in Iraq.”’ Smack! ”People want to understand more about a man or a woman in that position having made what we now can look back on as a mistake.” Smack! ”How did you get there, and what does that tell me about you?” Smack!

Suddenly, McDonnell glances down at the poor utensil. A wave of mild embarrassment washes over her face as she drops the fork, which hits the plate with a loud clang. She bursts into a gale of sunny, self-deprecating laughter, and returns her attention to the breakfast awaiting her at a cafe table overlooking the Santa Monica seashore.

It’s a relief to see McDonnell so lighthearted. After all, things have been mighty grim for her alter ego as Battlestar heads into its cataclysmic season finale March 25 (10 p.m.). Responsible for the very survival of humanity after attacks by the android Cylons have decimated all but some 39,000 human souls, President Roslin revealed this week that her terminal breast cancer, once thought to be cured, has returned. Still, Roslin has never felt more vital — to the show, to its die-hard fans, and, it appears, to McDonnell. ”[Roslin] has been a phenomenally important person [to me],” McDonnell says. ”When the good characters come along, they call you to represent them. Laura has called me into action.” And none too soon. McDonnell’s last truly substantial role was in the John Sayles drama Passion Fish. In 1992.

The dry spell, at first, was self-imposed. McDonnell took a break from acting to have a second child with her husband, actor Randle Mell, 55. (They live in Los Angeles with their daughter, 19, and son, 13.) Even though Dances With Wolves and Fish both won McDonnell Oscar nods and wide acclaim, ”when I came back,” she begins, ”it was one of those classic experiences in a career of a woman in Hollywood where it seemed like you were 37 for a decade, and suddenly you’re in your mid-40s and beyond. It was a lot harder to find unique roles.”

So hard that McDonnell, now 54, thought seriously about undergoing that other classic experience of women in Hollywood: the face-lift. ”I really do deeply understand the pressure that women are under, actresses in particular.” However, she says she changed her mind partly because her husband gently pointed out, ”Your entire career has reflected the common woman. You think [plastic surgery’s] going to get you more work?”

In fact, one of those common women helped land her the Battlestar gig: In 2001’s Donnie Darko, McDonnell had a minor role as a suburban mom. ”How [show exec producer Ronald Moore] got from Rose Darko to Laura Roslin…no idea,” McDonnell says. ”But there was something in [this] normal woman who has a lot more potential than she’s been able to articulate within the confines of [her] position.”

Although she means Rose Darko, McDonnell could just as easily be speaking about herself. Before shooting Battlestar‘s pilot, Moore created a detailed history of Roslin’s life on her home planet before the initial Cylon attack; central to that bio — not all of which has been revealed to viewers — was the fact that before her own cancer diagnosis, Roslin witnessed her mother succumb to the disease. Only after he’d cast McDonnell did Moore learn that the actress’ mother had also died of breast cancer. ”It was one of those whoa! kind of moments,” Moore says. ”You realize that there are these currents that sometimes carry people and projects together, that it was sort of meant to be…. There is a lot of Laura in Mary, and Mary in Laura.”

Even exploring Roslin’s hardest decisions — faking the death of a child, fixing an election, consenting to the torture of her political enemy — has enriched McDonnell’s understanding of herself. ”She’s released me, in a way…. This part has taken me [and] Laura — we’ve gone together — into understanding the levels on which a great deal of the powerful people on the planet are thinking and need to be thinking in order to survive this very dark time.”

With production on the fourth season set to begin in May, McDonnell says, ”I feel very satiated.” But for how much longer? At press time, Sci Fi has ordered only 13 new episodes. ”Oh, my gosh, how does one move on from Battlestar?” she says. ”Because having had the opportunity to delve into these issues and try to articulate them, I don’t want to stop.”