Mama Grizzly is clawing back at Levi Johnston ... claiming Bristol Palin's baby daddy straight up LIED when he claimed her family has been actively trying to block Levi from seeing his son, Tripp.

Sarah and Todd Palin have issued a statement to TMZ ... saying, "We have never hidden Tripp from Levi or discouraged Levi from spending time with him. Any suggestion that we have is false and contrary to our core beliefs."

The Palins add, "The last time either of us recall a conversation with Levi was in the summer of 2010 when Levi sat down at our house with us and personally apologized about lies he told to the media about our family. Neither of us have talked to him since that day."

The Palins are referring to the statements Levi made on "TMZ Live" this week ... when he accused the entire Palin clan of hatching a diabolical plan to keep him away from Tripp ... and said Sarah is the one pulling the strings.

But the Palins say Levi is full of moose droppings ... telling us, "We are disappointed that he continues to tell falsehoods about us to garner media attention. We encourage Levi and all non-custodial fathers to be fully engaged and to positively and fully participate in their children's lives. This includes not making misstatements about his child's grandparents."

Say what you will about 21-year-old Levi Johnston, but his sperm is world class -- he's gotten another girl pregnant out of wedlock.

Sources tell TMZ ... the lucky woman is Sunny Oglesby, a 20-year-old school teacher from Wasilla, Alaska. Levi has been dating her for just over a year. We're told she's in the very early stages of pregnancy -- less than 3 months.

Sunny isn't showing, which may be why Levi hasn't told someone else his secret -- and that would be Bristol Palin, his other baby mama.

Levi is telling friends Sarah Palin and Todd have completely alienated him from his son Tripp, and he barely sees him as a result. Levi says Sarah and Todd have lied to him, telling him Bristol and Tripp were out of town when they were not.

As a result, we're told Levi is "so excited" about starting his new family.

NBC has countered ABC's move of bringing Katie Couric to "Good Morning America" this week by announcing Sarah Palin will co-host "Today" this Tuesday. 

On their website, the peacock said that Palin will "reveal a different side of her than you've seen before." NBC is also promising that "a surprise legend will return to the broadcast Monday morning."

Palin and Couric are forever linked from their infamous interview in 2008 when Couric hosted "CBS Evening News."

The interview is widely credited for destroying Palin's credibility ... probably forever.

Call her Sarah Pa-LIN ... because the former Vice-Presidential candidate is the new Knicks' sensation's biggest fan -- even showing off her brand new "LINSANITY" t-shirt on the streets of New York today.

According to Sarah, Jeremy Lin is everything America stands for -- calling him "an American story ... uplifting, positive ... he unifies our country!"

But when it came to deciding between Lin and Tim Tebow -- Sarah reverts to politician mode, telling us she can't decide between the two ... she loves them both. Lame.

So we gotta ask ...

Sarah Palin believes her TWO jailed stalkers are still very much a threat ... and she's begging an Alaska judge to extend the restraining orders against them for another 6 months.

TMZ broke the story ... Shawn and Craig Christy, a father and son duo from Pennsylvania, were locked up in Alaska back in August for allegedly threatening to kill Sarah, her family and her friends.

Sarah had obtained restraining orders against the men ... but they were only temporary and will expire in November.

But Sarah has launched a preemptive strike ... filing a formal request to extend the order into 2012.

Sources connected to the case tell us ... the men are still waiting for their trial ... and will remain behind bars until a court date is scheduled.

If Sarah's request is granted, the men will be barred from having any contact with the Palins in the event that they are released.

A judge is expected to rule on Sarah's request sometime within the next few weeks.

Sarah Palin just announced she's not running for President of the United States.

She made the announcement via a statement to Mark Levin, a conservative radio talk show host.

Palin said, "After much prayer and serious consideration, I have decided that I will not be seeking the 2012 GOP nomination for President of the United States."

Palin added, "In the coming weeks, I will help coordinate the strategies to assist in replacing the President, re-taking the Senate, and maintaining the House."

There's nothing homophobic about Bristol Palin's heated exchange with a heckler last night -- according to her rep ... who claims Bristol was only defending her mom, Sarah Palin.

A rep for Bristol tells TMZ, she "was approached in a confrontational and inappropriate manner when two men aggressively shouted expletives aimed at her in reference to her mother. Bristol responded to the unprovoked verbal assault by calmly standing her ground and defending her family."

As we previously reported, Stephen Hanks yelled, "Your mother's a whore" -- prompting a face-to-face argument during which Bristol shouted at Hanks, "I just know you are" a homosexual.

The rep believes there was nothing bigoted about Bristol's words -- saying, "The situation ended with no incident, and accusing her of homophobia is completely unfounded and totally misstates her views."

TMZ tracked down Bristol Palin's heckler -- the one who screamed, "Your mother's a whore!" at a West Hollywood bar last night, and he's not ashamed at all.

Stephen Hanks is a 47-year old L.A. consultant who would not say what he consults on. He did, however, tell us this was not a setup.
 
As for Hanks' thoughts on Bristol's comment -- jumping to what turns out to be the correct conclusion that he's gay -- he has more choice words for Sarah's little girl.

Bristol Palin stood face to face with a very ANGRY Sarah Palin hater at the Saddle Ranch on the Sunset Strip last night ... after he screamed at her, "Your mother's a whore."

It all went down after Bristol rode the mechanical bull -- when the man shouted, "Did you ride Levi like that?"

During the confrontation, the man called Sarah "evil" -- and Bristol replied, "Is it because you're a homosexual and that's why you hate her?"

The man responded, "Pretty much ... and why'd you say I'm a homosexual?"

Bristol shot back -- "Because I can tell you are."

Bristol -- with her reality TV crew in tow -- eventually stormed out of the bar with her friends.

Sarah Palin finished behind a no-name in her Iowa run ... and it was still a very impressive showing.

Actually Palin -- who is not a declared Prez candidate -- ran a half-marathon in the Storm Lake, Iowa. 

She finished second among women 40-49, with a respectable time of 1:46.10.

Palin ran the 13.1 mile race using her maiden name -- Sarah Heath. 

As she says ... "Well, I guess ya' can stick that in your lower 48."

Levi Johnston's little sister HATES Bristol Palin ... calling her "evil" and a "sociopath" in a new Playboy interview. Oh, and she also gets naked.

19-year-old Mercede Johnston (above left) just WENT OFF about the entire Palin crew -- calling Sarah Palin a bad mom who's "never there for [her kids]" ... adding, "She doesn't make her kids go to school. She'd rather parade them around and put on a show, at book signings or conventions."

As for Bristol -- "Everything is about her, her, her. She has to have her own way. She'll be supersweet and then she turns into the most evil person I've ever known ... Honestly, she is the meanest person."

Mercede adds, "I didn't know someone could be so vindictive and evil ...[She's] a sociopath. She doesn't think anything she could do or does is wrong."

Mercede also claims Bristol and Levi PLANNED their pregnancy -- saying, "They were trying to conceive for months."

And for good measure ... Mercede explains why Sarah would have been a TERRIBLE president saying, "I think she'd have had a mental breakdown if she was elected [president] ... She can't even answer Katie Couric's questions."