It was a classic three minutes of television — Joe Cocker and John Belushi on stage together. Belushi, one of the regulars on NBC's "Saturday Night," does an uncanny impression of the twitchy-armed, beer-bellied, pug-faced, hoarse-voiced British singer; a while back on "Saturday Night" we got a glimpse of his Cocker persona as Belushi staggered on camera at the end of a song by Leon Russell, Cocker's ex-touring partner.

And, sure enough, on October 2 when guest star Joe Cocker hit the stage for "Feeling Alright," Belushi was there with him. The two were dressed in identical tee-shirts and suits and, vocally, it was hard to tell who was imitating who. They traded verses and sang together; by the end Cocker was copying Belushi's Cockerisms.

In his dressing room afterwards, Cocker told Rolling Stone that he'd enjoyed the duet, although, "I still think he's horrible." On the air, Belushi tried handling Cocker a can of beer. "He wanted me to pour it over his head," said Cocker, "but I think I should've poured it over me own head." Belushi's comment: "I love that man."

At a party after "Saturday Night" — where guests included Mick Jagger and Ronnie Wood (who saw the show), Jack Nicholson, Paul Simon and show host Eric Idle of Monty Python — Jagger was asked if he'd now consider getting into the same stage with would-be Stone Steve Tyler of Arrowsmith. "I'm ready to mix it up with Steven Tyler anytime," said Jagger. "Fact, we met in Los Angeles and spent some time together." Doing what, imitating each other? "Nah," Mick said "We sang together. We sang country songs."

Jagger was in town with the rest of the Stones, sorting through tapes of their spring European concerts. The boys want to put out a live album…Also, Mick has produced some tracks for John (Mamas and Papas) PHILLIPS. The collaboration could lead to an LP.

The Los Angeles Tennis Club was the scene of the Eagles' charity tennis festival October 3. About 2,000 people showed up — but the Eagles didn't. Glenn Frey, as it turns out, is the only tennis player in the group, and he was still nursing a torn ligament in his ankle that he'd suffered on the courts. Anyway, he and the others, in a hurry to wrap up work on their new album, were in Miami mixing tracks.

However, Keith Moon, Linda Ronstadt, Helen Reddy and members of Chicago did show up to whack the ball around. Some of the players were pretty good, including Tim Weisberg, Rick Nelson and Chicago's Bobby Lamm. Then there was Ronstadt, who looked like she was on foreign turf. She and partner Minnie Riperton lost dismally to Helen Reddy and Olivia Newton-John, as the referees admonished, "Girls, you don't rotate, this isn't volleyball." And Moon was good for the usual yuks, taking the court for his "comedy match" with Mark Volman wearing a helmet and brandishing his racket like a machinegun.

The festival, which was proposed by a lawyer to the Eagles, raised more than $20,000 for L.A.'s Concern Foundation for Cancer Research.

Paul McCartney and Wings recent benefit concert for the sagging city of Venice drew 25,000 people to the Italian city's historic St. Marks Square, and raised $50,000. It also succeeded in making the Square sag a little more into the canal — a couple of paving stones collapsed under the weight of the crowd and water seeped through.

Alice Cooper, who liked Acapulco's Carlos 'in Charlie's dining spot so much he got married there this spring, is one of the owners of the new L.A. franchise. The 200-seat Sunset Strip restaurant opened this month amid a parade of Rolls Royce Silver shadows in the circular driveway and glitter harlots in the bar.

Alice was there — with a 24-member party that included Carlos and Carlito, Bernie Taupin, Micky Dolenz and fashion designer Nudie. They had their pick of such entrees as Pork Jalapena, Drunk Sea Bass and Inflation Steak (for $9.50).

Earlier, Alice had explained his gourmet foray: "What do we have in L.A. — Hamburger Hamlet? I just wanted a place to go."