In Detroit, Ed Asner did three interviews, and all three began with the interviewer saying, "You know Ed, you remind me of my first city editor."

Before that, TV's Lou Grant was in Chicago on his current tour promoting Medic Alert. He met four more newspapermen there, and each one of them in turn said, "You know, Ed, you remind me of my first city editor."

Last year he met Walter Cronkite and Eric Sevareid at a big TV bash, and one by one they came up to him and said, "You know, Ed..."

It's true. He IS everybody's first city editor, the American mythic hero with the temper of a hibernating bear whose cave has been broken into, and just under the surface a heart of pure caramel.

When the photographer asked him to take off his glasses, he growled, "You takin' a picture of Ed Asner or Lou Grant?" And then let the guy boss him around like a fashion model.

With the authority he shows as city editor of the fictitious Los Angeles Tribune in the series, you just know that Asner must have been a real newspaperman himself. You're right: He was feature editor for the Wyandotte High School Pantograph in Kansas City, Mo.

"I'm a lost Journalist" he said.

Of course, he studied for the part, reading a 5-foot stack of transcripted interviews with newsmen all over the country. Some others in the cast attended journalism classes at UCLA, and every week a battery of Los Angels Times people is either actually on the set or available for a panic call.

Maybe this attention to detail is what gives the show its sharp sense of realism, the slight air of raffishness and unpolished shoes that one finds in every real city room. Maybe it's Asner's powerful presence, his palpable feeling of being responsible for his people, of worrying over them even as he chews them out.

Asner himself would probably say it's the scripts, which week after week reach a level that most shows merely aspire to.

He is proud of the loose ends in the stories, the refusal to wrap up each plot in a perfect package. In one show, Lou Grant manages after much struggle to win another chance at a job for a luckless Vietnam veteran. He rushes out to find the man, but his street pals say the guy took off and they don't know where he is. The End.

"We were relly worried about changing over from that comedy format on the Mary Tyler Moore Show," Asner said. For seven years he had played Lou Grant the TV news executive, and in all the history of spin offs, no one had ever tried to turn a comedy character into a serious dramatic actor.

"We went from a three-camera halfhour comedy to a one-camera full hour drama. At first the plots were erratic, there'd be a good one and then a terrible one, and besides the audience wasn't ready for the switch. Even CBS billed us in their promos as a comedy.

"In fact, the whole thing was impossible. But we didn't know that. We're pretty good. I'll say one thing, I'd never try that stunt again."

He is finished shooting for this season and is touring for Medic Alert, which he likes because it is nonprofit and useful "and you get a nice piece of jewelry too."

Grinning, he waggled the Medic Alert bracelet engraved with his blood type, the phone number where his medical history can be obtained, and the fact that he has no allergies or special medical problems.

"It used to be just people with diabetes or durg allergies, but now it also can specify that you can take any treatment. These days with joggers who collapse, the unidentified patient is a real problem. Emergency doctors have to find out if you're epileptic or wear contact lenses or have a pacemaker, and that takes time."

Next month Asner begins work on a TV movie with Anne Jackson, "The Family Man." Then he's off to Toronto for location shooting, and various other projects will keep him busy until he steps back into his Lou Grant suit in June. It is this succession of one-shot roles and public service spots that has kept him from feeling stale as Lou Grant. He has played everything from Mister Dooley to God.

He admits he hadn't seriously thought of acting until his roommate at the University of Chicago talked him into reading for "Murder in the Cathedral." He wound up playing Thomas a Becket, the lead.

"Wellll," he waved it all away, "I was beginning my first affair at the time, and I guess it was just too heady a wine to resist."

That's the thing about Ed Asner: You have to keep reminding yourself that he really isn't a city editor, and it's getting harder to do all the time. Just the other night he fuzzed up the distinction still more by being named an honorary member of Sigma Delta Chi, the national journalism society.

And he lectured us reporters. We shouldn't be such elitists, he said, interested only in our own privileges and fiefdoms instead of acting as agent and witness for the public.

He sounded just like my old city editor.