The way Marvin Gaye figured it, if Lem Barney and Mel Farr of the Detroit Lions could sing with him on a landmark recording, the Motown superstar could play in the NFL.

Forty years ago this summer, he set out to make it happen.

“There’s no question that if he had started out at an early age like most of us, he could have been a fine ballplayer,” Barney says. “Marvin had a lot of heart, a lot of will and stick-to-itiveness.

“He just didn’t have the skills.”

Not in football, anyway.

But that didn’t stop the 6-foot-4 Gaye from pursuing his dream — with the help of his football-playing friends.

Barney and Farr, the NFL’s defensive and offensive rookies of the year in 1967, had befriended Gaye in 1968 after Barney knocked on the singer’s door to introduce himself.

It was a difficult time for Gaye. Tammi Terrell, his duet partner on a string of 1960s hits including “Ain’t No Mountain High Enough,” had collapsed into his arms during a 1967 concert. Later diagnosed with a malignant brain tumor, she died in March 1970.

“Marvin really went into a stupor, and both Mel and I would go over and try to keep him encouraged,” Barney, 64, says from his home in Commerce, Mich. “And then one day he says, ‘Come on, let’s go by the studio.’

“We thought like always that we’d just sit and watch him perform. But he said, ‘Lem, you take this part,’ and, ‘Mel, you take this part.’ And as a result, it got us a gold record.”

The song they laid down, “What’s Going On,” was perhaps the most important recording of Gaye’s career, establishing the singer as a significant artist and not merely a hitmaker.

“‘What’s Going On,’” notes the All Music Guide, “was a new kind of protest song, a sugar-coated pill which surveyed the troubled landscape of an America torn apart by war, poverty and prejudice, but reported its findings not with anger and recriminations but with compassion and tenderness.”

It opens amid a party atmosphere, with Barney, Farr and others speaking scripted one-line greetings such as, “Hey, what’s happenin’?” and, “Brother, what’s up?”

The opening “set the record in a specifically black context,” author Steve Turner wrote in his 1998 Gaye biography, “Trouble Man.” “This was no longer just the ‘sound of young America,’ this was the sound of black America, and for the first time Marvin sounded as though he was speaking in his own voice.”

Motown executives, however, were said to be unmoved, company founder Berry Gordy reportedly dismissing “What’s Going On” as overly political and a tough sell.

The single remained unreleased for six months while Gaye, indignant, refused to record anything else.

It was during the impasse that Gaye, 31 at the time, set out to join the Lions as a wide receiver.

“He transformed a master bedroom into a universal gym and bulked up from about 180 pounds to about 210,” says Barney, a longtime pastor and executive at a Detroit hospital. “He ran every day and worked out. He was ready.”

Though he had never participated in organized sports, the singer believed he was a gifted athlete.

“I was always a sports fan,” he told David Ritz, author of the 1985 Gaye biography “Divided Soul,” “but I was determined to play for real. I knew I could. . . .

“You see, I had this fantasy: I was in the Super Bowl, with millions of people watching me on TV all over the world, as I made a spectacular leaping catch and sprinted for the winning touchdown.”

Through Barney and Farr, a former UCLA star, Gaye knew most of the Lions and had met their coach, Joe Schmidt.

“So Marvin went in to talk to coach Schmidt about it,” Barney says. “Schmidt asked if he had any film of when he played in high school or college and Marvin hung his head and said, ‘I didn’t play in high school. I didn’t play in college.’ So Schmidt said, ‘What makes you think you can play professional ball?’

“He said, ‘Coach, I just believe the first time I touch the ball I would score a touchdown.’ And Joe said, ‘I like your enthusiasm, so let me think about it.’”

Schmidt says he told the singer, “If I could sing like you, I certainly wouldn’t want to play football,” believing that Gaye and Barney were joking when they first met with him. Only after Gaye returned to meet with the coach a second time, this time unescorted, did Schmidt realize he was serious.

Still, Schmidt was unwilling to put the singer in harm’s way and quickly rejected the idea as unworkable.

In January 1971, Motown finally released “What’s Going On,” which soared to the top of Billboard’s R&B sales chart. An album of the same name, released later that year, also topped the charts and was hailed by critics as a pop music masterpiece.

On April 1, 1984, a day before he would have turned 45, Gaye was fatally shot by his father in Los Angeles.

Eight years later, Barney broke into song when he was inducted into the Pro Football Hall of Fame.

Gaye, of course, never made it that far, but his stirring version of “The Star-Spangled Banner” at the 1983 NBA All-Star game linked him indelibly to sports nonetheless. Twenty-five years later, Coach Mike Krzyzewski played it for the 2008 U.S. Olympic basketball team as inspiration.

“He was just a tremendously great musician,” Barney says of his late friend, “and one of the greatest guys you can imagine.”

jerome.crowe@latimes.com