The love child of Yankee superstar Randy Johnson yesterday broke her silence for the first time to describe how the pitcher coldly responded to letters she sent him as a little girl pleading to meet him.

"I would get cards back from him with just his signature - 'Randy,' " said Heather Renee Roszell, 16, who bears a striking resemblance to her "Big Unit" father.

The teen said she stopped writing to her dad after awhile because "I never got [more of] a response, so it got to the point where I didn't want to deal with not getting the response."

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She said she can't even bring herself to watch her famous dad pitch on TV anymore.

"I don't have a relationship with him," said the pony-tailed teen who, at 6-foot-1, inherited her 6-foot-10-inch dad's towering height.

Johnson's daughter appeared uncomfortable answering questions about her absent, 42-year-old father while standing outside her family's home in Langley, Wash.

She shrugged when asked what the $16 million-per-year pitcher could do to make up for lost time.

As she spoke, her mother and Johnson's ex-girlfriend, Laurel Roszell, stood at her side.

"The only thing Randy can do is step up and do what's required," said Roszell, 46.

"He needs to be an adult and take a big step. It's about Randy and Heather, not Randy and Laurel. How can he not [meet her]? She's his biological daughter. That's the connection, and she needs it."

The story surfaced Monday, after news broke that Johnson - who has since married and had four kids by his wife, Lisa - last month filed a legal motion against Roszell.

The hot-tempered hurler is seeking to recoup almost $100,000 that he laid out in day-care expenses - plus back interest - for Heather over the past eight years.

Johnson claims that Roszell failed to document on a quarterly basis, as required by a 1998 child-support agreement, that the money actually went toward Heather's child care.

Roszell denied the charge, asserting that Johnson filed the action in a snit only after she asked that he pay for a truck, computer and college-credit courses for Heather, on top of $5,000 per month he already pays in child support.

But Roszell added that there's another motive driving Johnson to sue her: He's still mad at her for dumping him years ago.

"It wasn't mutual," she told The Post this week of their breakup.

The mom refused to elaborate, saying only that her decision to dump the then-budding superstar was "personal."

Roszell explained that her best childhood friend was Johnson's sister, Cathy, and that she and the pitcher had known each other for years before they began dating.

But when they started going out, his now-infamous mercurial temper began to flare, she said.

She finally dumped him just before Heather's birth, when he was playing for the Montreal Expos.

Johnson has seen Heather only once - right after she was born - despite the fact that a custody agreement gives him "reasonable visitation rights," Roszell said.

She claimed said she has spoken to him just once since then, after she sought child support from him in 1998.

She bitterly recalled that he demanded a paternity test.

Even after DNA testing proved that Heather was his daughter, "it was still a struggle" to get him to pay adequate support, she said.

Finally, she said, "I got tired and said OK" to their agreement, which forced Johnson to pay her $30,000 in back support, his monthly support until Heather turns 18, $750 a month for day care, and money for college.

Heather didn't attend high-school classes yesterday amid the media attention over her newly revealed status as Johnson's daughter, something she says she has known all her life.

Heather said she avoids watching her dad on TV because of bad feelings - although she and her mom did watch him win Game 7 of the 2001 World Series for the Arizona Diamondbacks against the Yankees.

At the Yankees' spring training camp in Tampa, Fla., yesterday, Johnson said he stood by an earlier statement that he has "fully, financially supported" Heather.

"It's a situation my family knew the whole time. It's a family matter. I want to keep it private," he said.

Asked if the hoopla would be a distraction on the field, he said, "I am ready to pitch."

Johnson's agent, Alan Nero, has told The Post that the pitcher sought the day-care repayment from Roszell only after she threatened to go to court to ask for additional child support.

The "motion that is being filed is a motion to protect Randy and the child because the mother continues to ask for more money," Nero said.

Nero also said, "Randy tried his best to have a relationship with her [Roszell] and her daughter, and it just didn't work out. It just wasn't meant to be."