O.J. Simpson said yesterday he's "fascinated" by the murder of Robert Blake's wife — and knows just how the Baretta actor feels.

Simpson — whose "trial of the century" held the nation transfixed following the 1994 stabbing deaths of his ex-wife Nicole Brown Simpson and her pal Ron Goldman — also offered Blake these tips: 

* Don't take a lie-detector test. 

* Don't dis your dead ex. 

* Don't watch TV. 

"I've got to admit, I was pretty fascinated when I first heard it," Simpson says in an exclusive interview airing on tonight's Extra (7 p.m. on WNBC/Channel 4). 

"And my first reaction was an immediate feeling of compassion for him because I knew what he was about to go through. 

"I was just saying, 'This poor guy. I hope they find out who did it right away' — because the next week or two is going to be horrible for him, being under that veil of suspicion," the former football great tells Extra in the back yard of his Miami home. 

Blake's wife, Bonny Lee Bakley, was gunned down in the front seat of his car on an isolated street blocks away from Vitello's restaurant in Studio City, Calif., where the couple had just eaten dinner. 

Blake says he returned to the restaurant to retrieve his gun — and then went back to the car to find his wife shot in the front seat. 

Simpson advises Blake to turn off the boob tube. 

"Don't watch TV, Robert," Simpson says. "I know that watching TV is only going to frustrate him. That's all it's going to do. 

"He really wants to go out and hit somebody, but you can't win doing that." 

Simpson was acquitted of the murders of his ex and Goldman, but was later found liable for the slayings in a civil suit. 

Along with a lot of been-there/done-that advice, Simpson also gently mocks Blake, quoting words to the theme song of the actor's hit '70s police show. 

"Yeah, keep your eye on the sparrow. Don't do the crime if you can't do the time," Simpson says, reciting the lyrics sung by Sammy Davis Jr. 

Simpson tells Extra the only parallels between his murder case and Bakley's slaying is that "[Blake's] famous, I was famous. I think that's the only real comparison." 

Simpson also says he and his lawyers never smeared his ex-wife's reputation. One of Blake's lawyers, Harland Braun, has been brutally blunt in painting Bakley as a gold-digger and grifter. 

"My attorneys never said a word about Nicole's people and people involved with her," Simpson says. "My lawyers never revealed any information about Nicole that her friends hadn't already revealed. 

"My lawyers were never the leader in any of that because they were told specifically, and we had a philosophy, nothing negative about Nicole." 

In fact, during Simpson's civil trial, his lawyer trashed Nicole and her past troubles during opening arguments. 

Simpson, who says he's a Court TV junkie, also tells Extra Blake shouldn't take a lie-detector test — citing the cases of John and Patsy Ramsey and Louise Woodward, the English nanny found guilty of manslaughter for shaking a baby to death. 

"I would recommend to everybody, if you ever find yourself in this position, do exactly what the Ramseys did and what Robert Blake did," he says. "A lie- detector test at this stage of the investigation can only hurt him, it can't help him. 

"Because if he passed, much like the English nanny who passed two or three of them in her trial up in New England, you don't hear about them. They don't mean nothing." 

Simpson also has this advice for Bakley's family. 

"I would say, keep an open mind and put as much pressure on the LAPD as they can to make sure they're going to charge someone — and that they charge the right person," he says. 

"In my heart of hearts, I don't know [if Blake killed his wife], but I'm going to give him the benefit of the doubt," Simpson says. "As far as I'm concerned, this man is innocent until a jury comes back and calls him guilty. 

"That's the way everybody should look at this guy — that's the American way."