WWW- Randy Johnson has a secret love child - and the Yankees superstar is playing hardball with the girl's mom, it was revealed yesterday.

The flame-throwing lefty, who makes $16 million a year, is suing ex-girlfriend Laurel Roszell for less than $100,000 in child-care payments for their daughter Heather, now 16, according to court papers revealed by The Smoking Gun Web site.

"Oh, really?" Roberta Roszell, Laurel's mother, told the Daily News yesterday when told of the lawsuit.

"That sounds like Randy."

The striking, tall and athletic-looking teen refused to talk when she came to the door of her family's home overlooking a picturesque bay in Washington State.

The Big Unit yesterday admitted fathering the child during an affair when he was a lanky rookie with a nasty fastball and a bright future.

But Johnson insisted that he has always tried to do right by the girl, despite his money dispute with her mother.

"I do acknowledge that I have a daughter from a previous relationship, which ended years before my marriage," Johnson, 42, said in a statement. "I have fully financially supported her and have made every effort to protect her privacy."

Laurel Roszell, 46, was working at the Lawrence Livermore National Laboratory in northern California when she started going out with Johnson, a California native, in late 1988.

She broke up with the future superstar midway through her pregnancy and called the daughter his "little dark secret" in an interview with The Smoking Gun.

Roszell said Johnson only saw the girl once, soon after her birth - and said he never made any effort to be involved in her life. "Nope, nothing, never," she told the Web site when asked about Johnson's relationship to the girl.

Court papers reveal that Johnson first agreed in 1997 to pay $5,000 a month in child support for Heather Roszell, plus another $750 in monthly day care expenses.

Laurel Roszell claimed things turned sour last year when she asked the all star to buy Heather a car and foot the bill for community college classes.

He fired back with the legal equivalent of a high and hard fastball - demanding that she return about $71,000 in day care payments, plus $26,000 in interest because the teen was too old to be in day care, legal papers show.

"My daughter is 16 and has not been in day care for at least five years," Johnson said in a legal affidavit dated Feb. 3. "[Roszell] should not receive a windfall for expenses she did not incur."

Roszell countered that she gave up income when she stopped working full time to spend more time with the teenager.

Johnson, known for intimidating opposing hitters with his icy stare and 100-mph fastball, became a born-again Christian in 1992 after the death of his father.

He married his wife, Lisa, soon afterward. The couple has four children.

The sometimes ornery 6-foot-10 hurler got off to a bad start with the New York media last year when he grappled with a photographer and a TV cameraman after signing with the Bombers.

Observers were befuddled that Johnson would file a lawsuit over what amounts to chump change for the millionaire - all while risking unwanted publicity on an intensely private matter.

He had an uneven season last year but is the ace of the Bombers staff and is penciled in to start on Opening Day.