WASHINGTON (AP) _ Country music star Mickey Gilley said Thursday he plans to perform with his band at a March 21 benefit in Buffalo, Texas to help a 6-year-old girl raise $200,000 to pay for a liver transplant.

Gilley said he was contacted by Rep. Joe Barton, R-Ennis, who told his wife about Myranda Murchinson's liver illness and asked if Gilley could help.

''My wife told me there was a little girl in need in Buffalo, Texas and asked if anything I could do,'' said Gilley, who has played to audiences around the world, including a White House appearance for President and Mrs. Reagan.

''When I found out the little girl needed help I said to myself, 'How about if this was happening to one of my kids and I couldn't afford it.' It just breaks your heart to see little kids suffering like that.''

Barton, who has worked with the Buffalo Chamber of Commerce to organize the event on March 21, said the entire day will be dedicated to raising money for Myranda's operation.

''This is an opportunity for people from all over 6th District to help this little girl,'' said Barton. ''If she doesn't get this liver transplant she's going to die.''

Gilley said he was told that organizers plan to charge $10 a ticket for admission to the benefit concert.

''I'm doing this purely as a donation, and if they can get lots of people ot pay $10 a ticket they'll be able to make some money for the little girl,'' he said. ''We don't get a chance to do a lot of charitable work, but when we do it's extremely gratifying.''