Irlene Mandrell, the youngest of the performing Mandrell sisters, believes she'll always be overshadowed by her two versatile siblings. But she's the only one seen weekly on television. She's in her fourth season on ``Hee Haw,'' the syndicated hour-long program of country music and corn pone humor. All three starred in the NBC variety show,``Barbara Mandrell and the Mandrell Sisters,'' which ran for two seasons ending in 1982. Now country music singer Barbara Mandrell is seen periodically on television specials while the remaining sister, Louise, is seen primarily in a TV shampoo commercial. Irlene Mandrell, in an interview between tapings on the ``Hee Haw'' set, said her sisters are tough acts to compete against. ``Barbara and Louise are great showmen,'' she said. ``It would be hard to top them.'' But she's moving in that direction with her comic sketches on ``Hee Haw,'' which is in its 21st season as one of the longest running TV shows in history. On the program, Irlene's featured segments show her as a telephone operator and a highbrow society figure, Beatrice Meadows Watson, also known as BMW. As the telephone operator, Irlene is scatterbrained much like her character on the old network Saturday night variety show. ``People are always commenting about the spot, `I hope I don't get you as an operator. The call would never get through,''' she said. ``It's fun to do,'' she said. ``You get to dress different and use a different accent.'' She also appears regularly in segments set in a general store and truck stop. Her tenure on the program is a return engagement of sorts. Twenty years ago, she was on the show as a drummer in Barbara's band. When not busy taping ``Hee Haw,'' Irlene makes personal appearances, does some emcee work and appears occasionally with her sisters at concerts. At those shows, mostly at conventions, she opens the act by singing a number or two. Then Louise sings and plays her fiddle, followed by a segment by Barbara before all three join together. ``There's some slapstick like on the old (network) show,'' she said. On that program, she often was portrayed as the dippy sister in comedy spots. ``I guess they thought I'm a little dingy,'' she said. ``I miss the show a lot. We really liked to work together. I miss them.'' After the show went out of production, Irlene had two acting roles in the ``Love Boat'' series. She also did some dancing and singing on a road show with the Marty Krofft puppets, who had been featured regularly on the variety show. Serious acting, though, is a career ambition. ``I love comedy and I'm trying to get more involved in drama. I'm capable of it. Anything that came up, I could handle.'' But for the past two years, career moves have been delayed by motherhood. ``I end up pregnant every time something is happening,'' she said. ``The last few years I've been mainly mothering which I love. They are No. 1, second only to God.'' Deric is 2, and Vanessa is about 1. Irlene was born into a musical family in Corpus Christi, Texas. She was raised in Oceanside, Calif., until the Mandrells moved to Nashville when she was about 12. ``Barbara was special, even in grade school,'' she recalled. ``To me she's always been a superstar. I remember our grandmother used to tell us not to pound on the piano, but she could tell even then that Barbara had musical talent. ``Barbara and Louise are both honest, soft hearted and wonderful.'' Barbara still does concerts and performs periodically in Las Vegas while maintaining a recording career. Louise, meanwhile, recently has been the opening act for comedian George Burns. The careers of all three are managed by their father, Irby, a former singer and guitarist. Their mother also is a former musician. Sam Lovullo, producer of ``Hee Haw,'' said Irlene has done well on the long running program. ``She came from a show where it focused on three people. She's adapted well with the `Hee Haw' gang.''