“I don't think America knows what a gay parent looks like: I am the gay parent," the entertainer tells ABCNEWS' Diane Sawyer in her first in-depth interview about her sexuality.

O'Donnell has three adopted children — Parker, 6, Chelsea, 4, and Blake, 2. — and says she is in "a committed, long-term life relationship" with her partner of about four years, Kelli Carpenter. She talked about her experiences as a gay parent publicly for the first time with Sawyer, hoping to bring attention to the issue of gay adoption and a Florida law that prevents gay couples from adopting.

‘I Totally Think I’m Gay’

There's no earth-shattering coming-out story, O'Donnell says, just a realization that dawned on her in a private moment.  "When all my friends in high school, my girlfriends, were going out to bars and picking up men and fooling around on the beach," she says, "I would get Diet Coke and I was the designated driver. So it was never like a priority for me. I never thought about it."  When she was 18, she thought about it. "I remember driving my car when I got my permit," she says. "I was alone and I was like, 'I totally think I'm gay.' Like I says it out loud in the car."

She first fell in love with a woman a couple of years later; but she also had male lovers. "It took me a while to understand and to figure out all that things that made me me, where I was most comfortable, who I was, and how I was going to define my life," she says. "And I found the coat that fit me."

Her sexuality never has been and is not now "a big deal" for her, she says. "Part of the reason why I've never said that I was gay until now was because I didn't want that adjective assigned to my name for all of eternity. You know, gay Rosie O'Donnell."

O'Donnell, who lost her mother when she was 10 and describes her father as "not very available," says being gay was not that big of an obstacle in her generally difficult childhood.

Still, she believes that being gay is incredibly challenging. "I don't think you choose whether or not you're gay," she says. "Who would choose it? It's a very difficult life. You get socially ostracized. You worry all the time whether or not you're in physical danger if you show affection to your partner. You're worried that you're an outcast with your friends and with society in general."

Florida Case Strikes a Chord

Though there has been speculation that she chose to discuss her sexuality only because her talk show will come to an end this May, the actress/comedian says that is not so.

"I wanted there to be a reason" to talk about her sexuality, she says. And when she learned about a Florida gay parenting case, she found that reason and has made it her cause.

Steve Lofton and Roger Croteau are raising five HIV-positive children, three of whom are foster kids. The couple were able to adopt the other two in Oregon. The family was thrown into disarray when the state of Florida told them they had to give up one of their foster children, Bert, whom they have raised for 10 years. Lofton and Croteau would like to adopt Bert, but under Florida law they can't, because they are gay.

When O'Donnell read about the Lofton-Croteau case, she thought about her adopted son Parker: "My Lord, if somebody came to me now and said … 'We're going to take him now because you're gay,' my world would collapse. I'm lucky to have adopted my children, not in the state that I live, Florida. I'm lucky, because otherwise I would be in danger of losing my children."

The Right to Parent

O'Donnell says her own experiences as a mother make her certain that gay people should have the right to be parents.

"I know I'm a really good mother. I know it. I'm a really good mother. And I have every right to parent this child," she said. "It takes a lot to become a foster parent … You have to really want to save a child who others have deemed unsaveable. And for the state of Florida to tell anyone who's willing, capable, and able to do that, that they're unworthy, is wrong."

Asked about President Bush's statement — as well as the staunch belief of many — that children ought to be adopted only by a man and a woman who are married, O'Donnell says: "He's wrong. President Bush is wrong about that. And you know, if he'd like, he and his wife are invited to come spend a weekend at my house with my children. And I'm sure his mind would change."

Being gay, she says, does not make someone a bad parent. Any while the children of gay parents may face some ridicule from their peers, O'Donnell thinks they can get past that.

"I do think the kids will get teased, and you know, in some capacity that's very sad, and eventually I think that will stop. … I'm not asking that people accept homosexuality. I'm not asking that they believe like I do that it's inborn. I'm not asking that. All I'm saying is don't let these children suffer without a family because of your bias."

The Foster Care System

O'Donnell is trying to keep the Lofton-Croteau family together, but she's also hoping to shed light on the hundreds of thousands of children who are lost in America's foster care system.

"I was stunned into action. I mean I never knew that there were half a million kids in foster care in America," says O'Donnell. "There are over 350,000 children with nowhere to go — children who are most likely aged out of the system, and go either directly on welfare or directly to jail. It stunned me as an adoptive parent."

With so many children aching for a family, she says, "I don't think that restricting the pool of adoptive parents is beneficial."

O'Donnell dismisses claims that children adopted by gay parents are more likely to be gay. As for her own children, she says she hopes they will be straight. "I do. I think life is easier if you're straight. I hope that they are genuinely happy, whatever they are. That if they're gay, they know they're gay and they live a happy life. But if I were to pick, would I rather have my children have to go through the struggles of being gay in America, or being heterosexual? I would say heterosexual."

After emphasizing how much easier it is to be straight than gay, she says she wouldn't change her own sexuality. "I think if I could take a pill to make myself straight, I wouldn't do it, because I am who I am, and I've come to this point in my life and I'm very happy."

Written for ABCNEWS.com by Rebecca Raphael.