By Sabrina Ford

NEW YORK (Reuters) - In the popular 1979 film "Kramer vs. Kramer," Meryl Streep's character walked out on an unhappy marriage. More than 30 years on, Streep plays a middle-aged woman struggling hard to keep a sex-starved relationship together in her new movie "Hope Springs."

The bittersweet comedy-drama brings Streep, 63, and Tommy Lee Jones, 65, together for the first time as a couple whose marriage has so lost its spark that they give each other a new cable TV subscription for their 31st wedding anniversary.

Desperate for a shake up, Kay (Streep) persuades a reluctant Arnold (Jones) to attend a week-long counseling retreat with a couple's specialist, played by Steve Carell, the former star of TV comedy "The Office." All three sat down with Reuters in a joint interview.

"You get acclimated and I think people lose heart in themselves. You feel your own limits as time goes on and it's nice to have someone else to blame it on," Streep said of Kay and Arnold's stale relationship.

Jones, better known for his dry-humored roles in the "Men in Black" action movie franchise, said: "People get bored. And lazy. They do look for someone to blame."

The movie, which opened in U.S. theaters this week, mines the romance-for-the over 50s territory seen in Streep's more exuberant 2009 comedy "It's Complicated."

Streep, who has won three best-actress Oscars, said the movie was aimed at a discerning, baby-boomer audience that doesn't "respond to the same sort of things that kids do. They're looking for something that used to be in films of their era, and they don't find it."

"IT BETTER BE FUNNY!"

As Kay and Arnold try to find their way back to each other, they stumble through a series of sexual exercises often as sad as they are funny.

That includes Kay experimenting with a banana and an intimate, but awkward, movie date with her husband.

"It better be funny!" Streep quipped of the sex-act scene. "It was uncomfortable for my knees. I have bad knees."

Streep's Kay is an unglamorous retail employee whose husband is a cranky accountant with a regimented lifestyle.

Each day begins with Kay frying eggs and bacon for her spouse and ends when Arnold falls asleep in his lounge chair watching TV before Kay wakes him to head to their separate bedrooms.

"There's always one person who's agitated and one who says, 'It's fine,' said Streep. "The drama is getting the one character to move the other to a place where they both discover how much they need and love each other."

Carell says that while age is a theme of the movie, the story is universal and the struggles Kay and Arnold face could be experienced by people of any age.

"I think it's about love," said Carell. "It's about relationships. It's about commitment. It's about an older couple, but a good story is a good story.

"Hope Springs" has a 78-percent positive rating on Rotten Tomatoes, a review aggregator website, with most critics praising the performances of the three lead actors.

Time magazine's Mary Pols said that it "isn't an exciting movie, not remotely ... but I couldn't look away."

Manohla Dargis of the New York Times was less enthusiastic, however, calling it "an awkward cross between a domestic comedy and a marital tragedy that's laced with laughs, soggy with tears."

(Reporting By Sabrina Ford, editing by Jill Serjeant and Philip Barbara)