A man revealed to his 9-year-old daughter that a Pennsylvania couple claims she is their child and was mixed up at birth with another infant, but he insists he will not allow tests to prove it.

Robert W. Mays, a 43-year-old roofing supply salesman, identified himself Wednesday as the father of the girl, Kimberly Michelle Mays. He said he decided to step forward for fear that she would be told by someone else who might frighten her."It took me a long time to realize the seriousness of this situation," he said. "At first, I thought it was a terrible joke."

Regina and Ernest Twigg of Langhorne, Pa., claim the girl was born to them but was swapped with another child soon after birth in 1978 at a Florida hospital. The girl they raised as a daughter died in August of a heart defect.

During a news conference, Mays said he told his daughter a week ago of the Twiggs' monthslong battle to require her to submit to genetic blood tests to prove her parentage.

"It was the most difficult thing I ever had to do in my life," he said. "For a moment there was panic in her eyes. She said, `Daddy, I don't want to move away.' Does it mean I'm not your little girl?" she asked.

Mays said he reassured the blond fourth-grader that he was her father and nothing would change.