Pop singing, Ruth Brown realized several years ago, isn't what it used to be.

"I knew something was wrong when agents started asking my age," recalls the 51-year-old singer."One guy even asked me if I was over 22. I told him we might as well stop talking right there.

"Vegas," she says sadly, "was becoming rock-oriented."

No sooner had she looked at herself long and hard, than she took some acting lessons and auditioned for "Guys and Dolls."

And today here she is in her first season as Leona, an outspoken school- teacher in "Hello, Larry," an NBC-TV sitcom starring McLean Stevenson as Larry Adler, a divorced disc jockey with two teen-age daughters.

In the '50s, Brown was a rhythm 'n' blues queen, turning out a steady stream of hits -- "5-10-15 Hours," "Mama, He Treats Your Daughter Mean," "Teardrops From My Eyes." Dubbed "Miss Rhythm," she sang with a gritty, infectious quality.

By the '60s her kind of singing was considered old-fashioned. She focused on raising two sons and being a homemaker.

After a divorce and a heart attack, the singer decided she'd better look for another line of work.

Brown, plump and sloe-eyed, got her acting break when producer Norman Lear saw her in Las Vegas performing in "Living Fat," a comedy.

"He said he liked it and came back the next night with Alex Haley and a group of about 20 people," she recalls. "Alex said he had to come see if I was the Ruth Brown whose records he used to buy. He told me Norman was going to audition me, and I said, 'Sure, Alex, I'll believe it when I see it.'"

The next thing she knew she was on a flight to Los Angeles for the audition. "I read the part," she says, "and McLean was cracking up. Everybody loved it. I was supposed to just have a one-shot deal. But the character became an integral part of the show."

Brown is holding court at Pier Seven Restaurant. Also sitting there is blues singer Eddie (Cleanhead) Vinson, who's appearing at the Howard Theatre with Brown, Oscar-Brown Jr., Reese Palmer and the Marquees and the Donald Watts Sextet in a "Pre-Christmas Nostalgic Concert."

A man walks up and it's instant recognition."John Miller, what are you doing here," says Brown loudly.It's John N. Miller, vice president of the United States Brewers Association, and she hasn't seen him in 16 years. t"This guy and I were children together in Portsmouth, Va.," she tells the assemblage.

"Every time I see John I think of Billy Grogan," she says with an impish smile. "Billy's father was an undertaker. And we'd always invite Billy to birthday parties because he'd bring good presents.

"Once he brought me a sailor dress. Then he saw me wearing it to church one Sunday and hollered, 'Give me back my dress.' He chased me to church and into the basement trying to tear that dress off me.

"Thinking about these things scares me. Makes you think things go in full circle."

Much of Brown's early career was centered in Washington. She was fired by bandleader Lucky Millinder while performing here. But she caught the eye of Blanche Calloway, Cab Calloway's sister, who was managing the Crystal Caverns (to become the Bohemian Caverns) in 1947.

After performing here, Brown went to New York and cut her first record in 1949. The hits and successful road tours followed.

"Boy, we played some places we had to run from and hide," she remembers. "One time, [singer] Jackie Wilson didn't show up in Kansas City. The crowd got mean and evil. We could feel the anger coming toward us. Bo Diddley and I had to leave the auditorium in a hearse. Somebody drove it right into the ballroom.

"Sometimes we'd be traveling down South and the KKK might stop us on the highway and make us perform. Stand there with guns on us.

"I was on a tour with Roy Brown and some other people. We were on our way to Atlanta and got stopped somewhere in the sticks. All of us driving Cadillacs with New York license plates. The police said somebody had just robbed a tractor-trailer of four Cadillacs.

"Everybody had proper credentials but Roy. His car was registered in his agent's name. They threw him in jail and kept him there. By the time he got of jail the concert in Atlanta was long over."

Though she's found a new career, Brown still sings, mostly around Los Angeles, where she lives. In her act, she does a segment -- "Where Have All My Friends Gone" -- dedicated to Billie Holiday, Dinah Washington and Ella Johnson.

One of her disappointments is that she never got to sing on a major TV show. In her singing heyday, she says, vocalists like Georgia Gibbs and Patti Page took her hits and homogenized them for white audiences.

"But I got my break now," she says. "And I've got to make the most of if."