Collins’s essay, in which he came out as the first player in a major American sports league while still pursuing his career, was published online by Sports Illustrated on Monday morning. It precipitated an outpouring of supportive comments on social media sites by his fellow N.B.A. players, former professional athletes and President Obama, among countless others.

Current players posting in support of Collins included Tony Parker of San Antonio, Steve Nash of the Los Angeles Lakers and Knicks guard Jason Kidd, Collins’s former teammate when both played for the Nets.

The Lakers star Kobe Bryant wrote: “Proud of @jasoncollins34. Don’t suffocate who u r because of the ignorance of others.” He added the hashtags “courage” and “support.”

There has been much debate about how such an announcement would be received on the professional sports landscape, and it remains to be seen how Collins, 34, will be treated when he steps on the court for the first time since coming out. He will be a free agent on July 1 but plans to pursue a new contract.

Bryant’s Twitter message was reposted more than 20,000 times in the hour after his post, with some reminding him that he once sparked a controversy, and received a $100,000 fine, for directing an antigay slur at a referee who had called him for a technical foul. Since that episode, Bryant has voiced his support for the gay community.

Outside the N.B.A., encouragement was posted to Twitter by President Obama and Michelle Obama, Bill Clinton, Martina Navratilova, Spike Lee, Michael Strahan and others.

Michelle Obama wrote on Twitter: “So proud of you, Jason Collins! This is a huge step forward for our country. We’ve got your back! —mo”

Athletes from other sports also took to Twitter to support Collins, including the retired tennis star Andy Roddick and the Hall of Fame running back Barry Sanders. Chris Kluwe and Brendon Ayanbadejo, two N.F.L. players who have openly supported gay issues, sent messages of support.

Robbie Rogers, the American soccer player who recently came out as gay, posted, “I feel a movement coming.”

Collins started the day with fewer than 4,000 followers. By Monday night, he had more than 60,000.

In contrast to that widespread support, the ESPN reporter Chris Broussard drew criticism for comments he made calling homosexuality “a sin” on the network’s “Outside the Lines” program.

Broussard took issue with Collins’s description of himself as a Christian because he was “openly living in unrepentant sin.”

He added: “I believe that’s walking in open rebellion to God and to Jesus Christ. So I would not characterize that person as a Christian because I don’t think the Bible would characterize him as a Christian.”

David Scott, a spokesman for ESPN, declined to comment on Broussard’s statements.

ESPN.com, like other sports Web sites, received an unusually high number of reader comments on stories about Collins’s announcement. On ESPN.com, many of the comments were strongly critical of Collins; some included gay slurs.

“We are monitoring as always with our standard approach,” Scott said. “We don’t pre-moderate, but we are reviewing comments, flagging those that cross the line and handling according to our policies.”

Chris Stone, the managing editor of Sports Illustrated, said that the magazine had prepared for inflammatory comments to be posted on its Web site as soon as Collins’s essay was published.

“We’ve been pretty careful about curating the comments on our site because it did get a little bit out of hand pretty quickly,” Stone said. But he added that the comments had been positive over all.

“When I look at the general response, I see a message of overwhelming support and admiration,” he said.

One of the few negative public comments from a pro athlete came from Miami Dolphins wide receiver Mike Wallace, who wrote on Twitter, “All these beautiful women in the world and guys wanna mess with other guys.”

Wallace followed with a posting saying that he was not bashing anyone but that he did not understand homosexuality. He ultimately deleted both messages and posted another clarification in which he apologized for offending people.

The rare negative reaction among N.B.A. players came from David West of the Indiana Pacers, who took issue with Collins’s introducing his race as part of the story. He chose to not elaborate when pressed by his followers.

One of the strongest messages of support among active N.B.A. players came from Kenneth Faried of the Denver Nuggets, who wrote: “Wow this is amazing all smiles. So so happy Jason Collins came out & announce he was openly gay all support over here.”

Jerry Stackhouse, a guard for the Nets and a former teammate of Collins’s, spoke to reporters before his team’s playoff game in Brooklyn on Monday night and said Collins had told him that “I’m probably about to become one of the most popular or unpopular guys in the next few days.”

“He’s definitely become popular,” Stackhouse said.

Stackhouse added: “I don’t think he’s crossed the line in any way. I’m going to support him 100 percent and will encourage other guys to support him.”

Miles away, in the Bronx, in a baseball setting, Stackhouse’s sentiments were echoed by Yankees pitcher C. C. Sabathia.

“Good for him,” Sabathia said of Collins. “He can be honest and not have to live a lie.”

Zach Schonbrun contributed reporting.