Jane Alexander doesn't intimidate easily.

In her long career, the actress, now almost 68, has tackled a series of daunting roles ranging from Eleanor Roosevelt to Calamity Jane and given performances that have earned her a Tony, two Emmys and four Academy Award nominations. She also navigated the treacherous political waters surrounding her tenure as head of the National Endowment for the Arts.

Still, Alexander admits she thought twice before joining the cast of "Tell Me You Love Me," an envelope-pushing new HBO drama series premiering Sunday, Sept. 9.

Her role as Dr. May Foster, a therapist counseling three very troubled couples, was a meaty one, but it also called for something unprecedented: a nude and explicitly simulated love scene with David Selby, the 66-year-old actor cast as her husband, Arthur.

"I knew it was a first, and also given my image with the public, I knew it was going to be hard for some people to absorb," the actress says. "The wonderful thing is that David and I go way back together. We did some plays together in the '70s and '80s, and we've known each other for a long time. We both are personally in long, very happy marriages.

"You know, people tend to believe those scenes, when they see them, are real, but they're not. They're acted. Our union doesn't even let us have any real sex, not that we would anyway. But just acting with someone like David, whom I have known for so long, it was fine. Those scenes are never easy."

Series creator Cynthia Mort acknowledges that the intimate nature of some scenes made casting the series a challenging process.

"But once people read the script and understood, they were excited," Mort says. "Even Jane's agent at first was like, 'Um, I don't know.' But Jane read it and called me the next day because she understood the character's journey. I told everyone, 'Guys, I have no interest in somebody walking across a room naked. That's not what this is about. And they all jumped in."

Clearly HBO is hoping that even if some viewers initially tune in for the skin, they will hang around to watch the personal dramas of the couples in therapy: engaged 20-somethings Jamie and Hugo (Michelle Borth, Luke Kirby), who are grappling with the prospect of lifetime fidelity; Carolyn (Sonya Walger), a corporate executive in her 30s, who is obsessed with having a child with her far more ambivalent husband, Palek (Adam Scott); and Dave and Katie (Tim DeKay, Ally Walker), a 40ish couple who clearly still deeply love each other yet have stopped having sex.

While viewers may gravitate to the couple closest to their own ages, it's hard to imagine that anyone could remain unmoved by the work of DeKay and Walker, who etch a double portrait so poignant and honest that it's almost hard to watch without feeling like a voyeur.

"Ally and Tim are incredible," Mort says. "They have such a connection. They really had something that so many people can see and understand and fall in love with."

Walker, best known to many viewers from her work in the NBC thriller series "Profiler," points out that, despite fairly extensive nudity, "Tell Me You Love Me" isn't really titillating.

"This is an exploration of real intimacy, and sex happens to be a part of real intimacy between people," she says. "At least for me, it didn't seem gratuitous ... so it has a very real feeling, which I think does upset some people. It didn't make me nervous.

"[One couple is] having sex where you're trying to get pregnant, which is not hot. [My character is] not having sex at all, which is depressing. And Michelle's having sex to hide behind because she's in pain. So it's not really there to titillate you."

Alexander says she was delighted to play an older woman who has such a rich, rewarding and complicated emotional life, something that isn't often portrayed on U.S. television.

"I thought that seeing the therapist at home was terrific, and seeing that she had a really good, long-standing marriage and they were still sexually active, complicated by a past lover - all of that appealed to me. They are flesh-and-blood human beings.

"I think my colleagues on this are so brave and wonderful, and they are just such good actors. They just do a great job."

Ten episodes have been produced for season one of "Tell Me You Love Me," but Mort says there are many more stories to explore if HBO orders a second season. And Alexander is ready and eager to revisit Dr. May Foster.

"I think there's a lot more than we can discover about the characters and the problems that people have," she says. "I think Cynthia is going to come up with another wonderful season."