FOR hours, NATALIE WOOD screamed for help while clinging to the side of a dinghy before the exhausted actress slipped beneath the waves and drowned.

And her husband Robert Wagner could have saved her if he had called for help sooner, says the lifeguard who pulled Natalie’s body from the water.

“Wagner could have saved his wife. But he didn’t,” said Roger Smith, a former Los Angeles County supervising rescue boat captain who headed a lifeguard team that helped in the search for Natalie that fateful morning more than 30 years ago. “Robert Wagner should be charged with manslaughter! I believe he is re­sponsible for her death!”

IN A WORLD EXCLUSIVE ENQUIRER interview, Smith broke a 30-year silence and revealed shocking never-before-heard details about the tragedy that has remained a mystery and is currently being reinvestigated.

At 5 a.m. on Nov. 29, 1981, para­medic Smith and his team were asked to help in the search of the waters off Catalina Island. He was onboard an L.A. County lifeguard rescue boat when Wagner came aboard and overheard authori­ties questioning him. Natalie had already been missing for many hours.

“I asked him what happened and he said, ‘She went out to re-tie a dinghy that was banging against the boat,’” said Smith.

“Robert Wagner added, ‘I don’t know what happened to her. She was missing after that and the raft is also missing.’”

A deputy sheriff asked why Wagner delayed calling for a search party sooner. Wagner’s answer stunned the cop and Smith.

The actor said he just had a few harbor patrol boats check other yachts in the area to see if Natalie was onboard one of them. He didn’t notify police and rescue teams sooner because a search by official agencies could result in an embarrassing public relations nightmare.

He said, Natalie “might be fool­ing around on somebody’s boat. She often does that.”

The astonished deputy took Smith aside and asked him: “Is that what he just said?”

Smith said his first thought was: “Too bad the famous must die because somebody might be embarrassed.”

When the empty dinghy was eventually found, a helicopter hovered nearby and spotted something beneath the water several hundred yards away. Smith’s rescue boat got there first. It was Natalie, just below the water. He gently lifted her body up and laid it down on the deck.

“Based on the condition of Ms. Wood’s body, I believe she survived for 3-5 hours hanging onto the side of the dinghy. She probably cried for help for hours,” said Smith.

“Her fingers were still pliable when she was pulled from the water, suggesting she had not been dead for hours.”

And on the side of the dinghy were scratch marks, indicating to Smith that the actress – who had a fear of the water – had desperately tried to claw her way back into the vessel, but couldn’t.

“I think Robert Wagner could have saved his wife,” said Smith. “But he didn’t.”

Wagner’s attorney, Blair Berk, said his client does not “have any new information” for a re­newed investigation by the LAPD into Natalie’s death – a move, he charged, that was prompted by publicity seekers trying “to exploit and sensationalize the 30th anni­versary” of the actress’ death.