NEW YORK — It all started with a slap for Matthew Rhys. Trying out for “The Americans,” he took one in the puss from Keri Russell.

This new FX drama, whose third episode airs Wednesday at 10 p.m. EST, focuses on two KGB spies posing as an ordinary American couple shortly after Ronald Reagan became president.

As Philip and Elizabeth Jennings, they have a comfortable home in a Washington suburb, two sweet kids, a travel agency they run and, by all signs, a solid piece of the American Dream. No one would suspect that they are Russian-born plants bent on burying the United States with subterfuge and brutality.

No one, that is, unless it’s their new neighbor, FBI agent Stan Beeman (played by Noah Emmerich with an infectious mix of cunning and dorkiness), who has recently moved in with his family across the street. He represents just one among the many threats of exposure, imprisonment or death they face daily.

“It’s an incredible balancing act to portray: the domesticity of their suburban lives and the struggle of their relationship as an arranged couple, and then the extreme spy stuff,” says Rhys.

“The balancing act is very difficult,” echoes Russell in a separate interview. “We’re spies, but how much do you play that reality? And how do you play the masquerade that you’re NOT a spy? There are so many layers to it.”

“The Americans” is a good old-fashioned thriller, set in a pre-cellphone, -Internet and -PC world where gumption counts as much as gadgetry in the espionage game, and where the world is a very anxious place yet handily divided between Good and the Evil Empire (as Reagan dubbed the Soviet Union).

Meanwhile, the series calls on viewers to root for Philip and Elizabeth as they risk everything to advance this “Evil Empire.”

But however driven in their partnership, they are butting heads. Elizabeth despises American values. She is fiercely devoted to the cause of Mother Russia. But Philip is torn: He doesn’t think the U.S. is such a bad place.

“That kind of disagreement is something I understand as someone who is not a spy, but as just someone in a marriage,” says Russell with a knowing smile.

For most viewers, Russell, now 36, needs no introduction. In 1998 she burst on the scene, complete with those flowing pre-Raphaelite curls, in the title role of “Felicity,” then followed up with the miniseries “Into the West,” films including “Extraordinary Measures,” “Waitress” and her upcoming horror flick, “Dark Skies,” and, alongside Will Arnett, the short-lived sitcom “Running Wilde.”

The script for “The Americans” arrived at Russell’s door just days after the December 2011 birth of her second child, Willa Lou, with carpenter-husband Shane Deary. Understandably, she wasn’t eager to rush back to work.

“But this show was so strange and complicated I couldn’t really figure it out, and I thought, `That could stay interesting and fun to do,'” she says. Besides, it conveniently substitutes circa-1980s Washington with New York locations. “It shoots near my house in Brooklyn. I can ride my bike to work.”

Still sylphic and long-haired, Russell makes an ideal Elizabeth Jennings, who, by turns, is a lovely wife and mother, a fearless operative and a rock-’em-sock-’em brawler.

And to hear her talk, Russell seems thrilled with her leading man.

The 38-year-old Welsh-born Rhys is best known from ABC’s drama “Brothers & Sisters,” where he played lawyer and gay man Kevin Walker. His credits also include the indie film “The Scapegoat” and the BBC miniseries “The Mystery of Edwin Drood.”

“He’s a real actor! I’m in awe of him!” says Russell. “We’ll be doing a scene and I’ll go, `Matthew’s doing all of THAT, and I’m just doing THIS! Arggggg!’ Between Matthew and Noah Emmerich and me, I’m the most boring TV person in the show.”

When those words are shared with Rhys, he bursts out laughing.

“She’s INCREDIBLE! She’s the total package!” he declares. “Her work ethic is huge, she takes the right things seriously and most of the other stuff, not. I wish she had a little more awareness of how good she is.”

Rhys was asked to come test opposite Russell based on his impressive off-Broadway debut in the 2011 revival of the modern classic “Look Back in Anger.”

“I was brought in for the infamous `chemistry read,'” he chortles, meant to see how he and Russell would mesh.

He was one of several prospects.

“In between them, I was pumping in the bathroom because I was nursing a new baby,” Russell laughs. “And then I’d come out and test with the next stranger. We were reading the scene in the laundry room from the first episode, where Philip presents the idea of defection.” (Philip tells Elizabeth: “We could get relocated, live the good life, and be happy.”) “My character is outraged that he would even consider it.

“Basically, there’s a slap in that scene,” Russell adds. “But when the first guy came in, I didn’t do it.”

Then it was Rhys’ turn. “The director said, `Slap him.’ So I went for it.”

Rhys picks up the story: “Strange as it may sound, she slaps incredibly well. In the same place every time, and never near your eye. The swing of her arm was incredibly violent, but her wrist remained soft, so there wasn’t much force behind it.”

Clearly, he and Russell connected.

“And now it’s become this ongoing joke,” he says. “Keri will slap me – not hard – just before a take, just to see how I react. I feel like Inspector Clouseau and she’s Cato. It’s a surreal feeling to have the demure, angelic Keri Russell wallop you across the chops at any moment. But it’s great!”

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Online:

http://www.fxnetworks.com

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Frazier Moore is a national television columnist for The Associated Press. He can be reached at fmoore(at)ap.org and at http://www.twitter.com/tvfrazier