NICOLE KIDMAN sparked rumors of a pregnancy when she was recently photographed hiding what appeared to be a baby bump, but sources tell The ENQUIRER that the Aussie beauty is NOT pregnant.

However, the 46-year-old actress IS planning to have another baby by surrogate in a desperate attempt to salvage her troubled marriage to country star Keith Urban, the sources add.

“Keith is hoping for a son,” an insider told The ENQUIRER. “And the plan is already bringing them closer together.”

NICOLE ALREADY HAS FOUR CHILDREN. She adopted Isabella, 21, and Connor, 19, during her 11-year marriage to Tom Cruise. She also had daughter Sunday, 5, naturally with Urban, and 3-year-old Faith came by way of a surrogate.

Meanwhile, rumors began to fly when a photo of Nicole was snapped on May 6 at the Sydney airport, after wrapping up filming “Strangerland.”

“She was hiding her belly,” said the source. “She covered up with her arm and held her blazer closed.”

As The ENQUIRER recently revealed, Nicole reportedly was facing a $175 million divorce showdown with Keith – a recovering cocaine and alcohol addict – over fears that he’ll stray while they are working on opposite sides of the globe.

What’s more, sources say the two have been doing a lot of long-distance arguing over the past few months – and she’s ripped into him over his onscreen flirting with fel­low “American Idol” judge Jennifer Lopez.

As her marriage problems mounted, Nicole also had to deal with a red-hot controversy over her new film “Grace of Monaco,” in which she plays the tragic princess. Grace Kelly’s kids – Prince Albert and Princesses Caroline and Stephanie – have repeatedly attacked the film for alleged inaccuracies and vowed to boycott it.

Adding to her stress, Nicole was heart­broken by the death of her closest pal of 25 years, designer L’Wren Scott – Mick Jagger’s girlfriend – who hanged herself March 17.

“Nicole has admitted that sometimes she feels like the world is caving in on her,” said the insider. “She hopes that she and Keith can add a son to the family, and that the little bundle of joy will help to put their marriage back on track.”