ORLANDO, Florida (Reuters) - An Eagle Scout whose defense of gay civil unions went viral in 2011 on YouTube plans to challenge the anti-gay policy of the Boy Scouts of America at its annual conference in Orlando on Wednesday.

Zach Wahls, 20, of Iowa City, Iowa, told Reuters he will present the Boy Scouts leadership with a petition signed by more than 280,000 people calling for the organization to end discrimination against gay youth and leaders.

Deron Smith, public relations director for the BSA, said on Tuesday that the conference and Wahls' presentation will be closed to the press and public.

Eagle Scout is the top rank attainable in the BSA and requires a major service project to demonstrate leadership, along with numerous merit badges.

The petition was launched April 17 on Change.org, the web-based social change platform, by Jennifer Tyrrell, 32, a former Boy Scouts den leader from Bridgeport, Ohio, one week after she was ousted because she is gay. The petition also calls for her reinstatement.

"The hope would be for them (the Boy Scout leadership) to see the vast amount of signatures ... There's going to be boxes and boxes and boxes to set the stage for (them to see) this is how many people agree with this, hoping to get the Boy Scouts to do the right thing," Tyrrell told Reuters.

Tyrrell, who will not attend the event, said she is not optimistic. But Wahls, whose defense of his lesbian mothers and civil unions before the Iowa House of Representatives has been viewed on YouTube more than 2.5 million times, said gay rights advocates are aware of many Boy Scout leaders who support change.

"I think it's a lot closer than people might expect," Wahls said, adding, "It's very clear that there's a lot of support even within the Boy Scouts of America ... What we're trying to do is make sure we give them some real credence so they know that they have external support, that there are a lot people that have their back when it comes to actually changing this policy from a national perspective."

SUPREME COURT RULING

Smith released a written statement on behalf of the Boy Scouts of America:

"Scouting values the freedom of everyone to express their opinion and teaches its members to treat everyone with courtesy and respect at all times. The BSA sets polices that are best for its organization and membership. The BSA welcomes all who share its beliefs but does not criticize or condemn those who wish to follow a different path," the statement said.

The Boy Scouts of America in 2000 famously won a 5-4 U.S. Supreme Court ruling allowing the organization to ban gays whose conduct, the Boy Scouts argued, violated its values.

Wahls, his lesbian parents and Tyrrell found that local Boy Scout leaders and parents accepted them regardless of the parents' sexual orientation.

"It was a complete non-issue after people got to know me and know my parents," he said.

Tyrrell said she was assured by her local cubmaster that her sexual orientation was not a problem and she was even drafted to be den leader.

However, later, when she became treasurer and pointed out some financial discrepancies in the books, someone told the pastor of the church that chartered her den that she was gay, and the Boy Scouts dismissed her.

"The fact is the (Boy Scout) organization is still run by a lot of older folks who grew up in a time and culture where quite frankly this was not something that was discussed," Wahls said.

On the Change.org web page hosting Tyrrell's petition, supporter James Dozier was one of several former scouts who posted comments critical of the anti-gay stance.

"It is stuff like this that really demeans all I worked for to become an Eagle Scout ... I am so grateful for everything the Scouts taught me and I am proud about being an Eagle Scout, but this really diminishes everything I accomplished," Dozier wrote.

The BSA is one of the biggest U.S. youth organizations, claiming some 2.7 million youth members and over 1 million adult volunteers at the end of 2011. It was founded in 1910 as part of the international Scout movement established in Britain by General Robert Baden-Powell.

(Editing by Jane Sutton and Eric Walsh)