BACK in the primeval days of country music, when the Grand Ole Opry was young, before there were country queens like Tammy Wynette and Dolly Parton, female singers in country music usually played a subordinate role. They were often part of a group, or their names were linked with a male star.

But Patsy Montana broke the rules and became a country star in her own right, pining for her "cowboy sweetheart" on radio and records, and in 1936 she became the first woman to sell a million copies of a country record.

"There were no other girl singers back then," says Montana. At 69, she still refers to herself as a girl singer. "People are always asking, 'Who were your influences?' And I think, and I have to say . . . Kate Smith. Now, she definitely was not my type. I admired her, but she certainly was not Western. But she was all there was."

Montana, nicknamed "The Yodeling Cowgirl," left her home in Long Beach, Calif., last weekend to help open "The American Cowboy" exhibition at the Library of Congress. Her song "I Want To Be a Cowboy's Sweetheart," her first million-record seller, is on the jukebox in the exhibition.

"After 'Cowboy Sweetheart,' Art Satterly, my manager --he discovered Gene Autry and Bob Wills, too--had me write so many songs with the word 'sweetheart' in them," Montana says. Hence, a string of hits, including "I Only Want a Buddy, Not a Sweetheart," "Me and My Cowboy Sweetheart," "I've Found My Cowboy Sweetheart."

"I had to write my own songs," Montana says, "No one knew how to write for a cowgirl."

Among the 200 songs from a recording career that spanned the '30s to the '70s were "Don't You Love Your Daddy, Too," "The Wheel of the Wagon Is Broken," and "If I Could Only Learn to Yodel."

Yodeling, in fact, became Montana's signature. "I never heard it called 'yodeling,' really," she says. "I grew up with the old Jimmie Rodgers records, and my mother would say, 'Get out of the house with all that hollerin'!' Your yodel is in the little break between your natural voice and your falsetto voice. You either have it or you don't.

"At the Library of Congress the other night I was taking pictures, and I saw Alexander Haig, and I thought, oh, I won't waste the film," Montana says. "But after I did my number he came up and hugged me and said, 'Oh, that yodeling drives me crackers!' I took his picture then."

Montana grew up with her 10 brothers near Hot Springs, Ark. Her real name is Rubye Blevins, but her stage name was a fortunate synthesis of Monty Montana, a world champion yodeler, and a trio she sang with in her early performing days. "We were called the Montana Cowgirls, and my name was Rubye and one of the other girls' names was Ruthie. It got confusing, so being the Irish one, they just dubbed me Patsy Montana."

Montana appeared in several western movies with "Singing Cowboy" Gene Autry, including "Colorado Sunset" and several shorts. "I never played the leading lady. I was always the ingenue--the tomboy part. He never kissed the leading ladies anyway, you know, they always kissed the horse!"

After the movies, Montana joined a Chicago-based group called The Prairie Ramblers, whose members all claimed to be born in Kentucky log cabins. Together, they appeared at nearly every county fair in the country, and became regulars on Chicago's National Barn Dance radio program. Montana remained a headliner on the show well into the 1950s.

Now, Montana says, she keeps busy recording and touring. She has a new record coming out soon, "with Waylon Jennings on 12-string guitar," and she makes two tours a year, one to the Midwest and the other in Europe.

"They like the traditional country sound over there," says Montana. "I think a lot of the English still think we're fighting Indians!"