Even on Capitol Hill, where working the crowd is a rite of political passage, they have to admire a pro like Minnie Pearl.

"You know, I feel just like my brother from Grinder Switch," said Pearl, grinning over her shoulder to the audience at the Subcommittee hearings. "They say he's like the bottom half of a double boiler: He gets all steamed up before he knows what's cookin'!"

In a five-hour whirl through Washington yesterday, the veteran of the Grand Ole Opry, hit congressional wives and the First Lady at a luncheon, and then took on the House Communications subcommittee.

"Back in Grinder Switch, we don't have that much interest in politics, 'cept one year when Cousin Nabob was runnin' for constable. Nabob went to see ol' Lem and said, 'Lem, I'm runin' against Seph Jones and I need your vote.' And Lem said, 'Nabob, I wouldn't vote fer you if you was St. Peter hisself.'

"Well, Nabob said, 'Lem, if I was St. Peter, you couldn't vote fer me 'cause I wouldn't be in your district.'"

Pearl understands constituencies as well as anybody in Washington, and hers has no district lines.

It covers 34 states and millions of listeners in the 750-mile broadcast reach of the Grand Ole Opry. It's for her "people" and WSM, the Nashville radio station which produces the Opry that Pearl came to testify. She came, not as the furbellowed and bonnetted Minnie, but as the well-groomed, Ward-Belmont alumna she is.

A proposed FCC rule would ban the so-called "clear channel" stations like WSM which have sole use across the nation of a single radio frequency, in an effort to encourage local radio service.Opponents of the bill, including the Opry listeners who mounted a heavy letter-writing campaign, argue that 26 million Americans living in "white areas" over half of the United States would have no nighttime radio service without the clear channels.

"I've spent 27 years travelling from one end of this country to the other, talking to the people," Pearl told the subcommittee, "and they have convinced me that WSM and the other clear-channel stations fill a need that smaller stations simply can't."

For the subcommittee, which has been struggling with the communications hearings for two years, Pearl's appearance afforded welcome comic relief. The members even "recessed for 30 seconds" while representatives Albert Gore Jr. and Bill Boner, both of Tennessee, posed with their arms around her.

"This isn't nearly as hard as I thought it'd be," she said laughing, and batting her eyelashes old-maid brazenly at Gore. "You're a nice man."

"Just one thing," said Gore. "I gotta hear it . . ."

"How-DEEEEEEE!"

Minnie Pearl was "born" in 1936 (her real life alter ego, Sarah Ophelia Colley Cannon, says she was born "a few years earlier than Minnie.

Back in the '30s. Cannon was touring the South producing amateur corn-pone musicals, picking up country stories and characters, as well as Minnie's impervious accent.

She joined the Grand Ole Opry in 1940, spreading the gospel of Grinder Switch (a tiny town which actually exists in Hickman County, Tenn.) and, her relatives. Her "folks" haven't changed much since the '40s.

"My brother-well, let's just say that when he says 'Howdy!' he's told you everything he knows.

"Uncle Nabob ain't exactly a failure. It's just that he started at the bottom and he likes it there."

"He says gettin' married is like gettin' into a tub of hot water-once you get used to it, it's not so hot."

These folks are her coverall constituency; and they are, as she and the appearance of a dozen photographers reminded the subcommittee, a power ful voting bloc.

Despite its general affability, it is a constituency which can get its dander up, as Pearl told the congressman in a pointed anecdote:

It seems an old farmer was in court trying to recover damages from the man who smashed his truck and killed the cow in the back. The defense attorney kept interrupting to shout, "Isn't it true that, immediately after the accident, you stated that you felt fine?"

"Now, wait a minute," said the farmer. "That man came straight across the median and hit me head-on. When the officer got out to look at my cow, he said, 'That poor beast is in bad shape,' and shot it in the head. "When he came around to ask me how I was, I said, 'I feel fine!"

"You see," said Minnie Pearl. "You always have to remember the frame of reference." CAPTION: Picture, Minnie Pearl by James K. W. Atherton