“I’m a 34-year-old N.B.A. center. I’m black and I’m gay,” Collins, who finished this season with the Washington Wizards, writes in the May 6 edition of Sports Illustrated. The magazine published the article online Monday morning.

With that statement, Collins became the first openly gay male athlete who is still active in a major American team sport. Other gay athletes, including the former N.B.A. center John Amaechi, have waited until retirement to divulge their sexuality publicly.

The announcement followed recent decisions by two other athletes — the American soccer player Robbie Rogers and the women’s basketball player Brittney Griner — to acknowledge that they are gay. When Rogers, 25, revealed last month that he was gay he also said he was retiring from soccer. (He has since indicated he may play again.) Griner, the No. 1 pick in the W.N.B.A. draft, will soon embark on her pro career.

Collins’s announcement was greeted with an outpouring of support from teammates, league executives and major N.B.A. stars, Kobe Bryant and Dwyane Wade among them.

“Proud of @jasoncollins34,” Bryant, the Los Angeles Lakers star, wrote on his Twitter account. “Don’t suffocate who u r because of the ignorance of others.” Bryant added two hashtags: “courage” and “support.”

Some of the N.B.A.’s biggest names followed suit, including the Lakers’ Steve Nash, Oklahoma City’s Kevin Durant, the Knicks’ Jason Kidd and San Antonio’s Tony Parker. Several teams sent out statements of support. Prominent coaches, including Boston’s Doc Rivers, who has worked with Collins, gave support in interviews.

However, one N.F.L. player, Mike Wallace of the Miami Dolphins, posted a comment on Twitter: “All these beautiful women in the world and guys wanna mess with other guys.” He later deleted the comment and issued an apology.

And on ESPN, the N.B.A. analyst Chris Broussard, citing his religious beliefs, said that living openly as a homosexual was a sin and that doing so was “walking in open rebellion to God and to Jesus Christ.”

But those comments were greatly outweighed by the supportive ones Collins received, particularly from his N.B.A. peers.

“The overwhelming positive reaction does not surprise me,” N.B.A. Commissioner David Stern said in a telephone interview. “Our players are actually knowledgeable and sophisticated on this issue, and our teams understand it completely. I would have expected them to be supportive, and they are.”

President Obama called Collins “to express his support and said he was impressed by his courage,” according to a tweet from the White House. Michelle Obama, on her Twitter account, called Collins’s announcement “a huge step forward for our country.”

Collins becomes a free agent on July 1 and intends to pursue another contract, which might be viewed as a truer test for how N.B.A. teams deal with a gay athlete. However, complicating that question is the fact that Collins, at 34, is a marginal player with limited skills, more valued for his locker-room presence than his play and not at the top of anyone’s list of players to sign. He appeared in just 38 games this season, which he split between the Boston Celtics and the Wizards, and was used sparingly.

Collins was never among the most skilled centers to begin with, instead relying on his size (7 feet, 255 pounds), intelligence and work ethic to carve out a niche after being drafted 18th over all in 2001.

In his Sports Illustrated essay, Collins alludes to his future status in the league: “I’ve reached that enviable state in life in which I can do pretty much what I want. And what I want is to continue to play basketball. I still love the game, and I still have something to offer. My coaches and teammates recognize that. At the same time, I want to be genuine and authentic and truthful.”

Zach Schonbrun contributed reporting.