In a speech in Atlanta to the Scouts' national annual meeting, Gates referred to recent moves by Scout councils in New York City and elsewhere to defy the ban.
"The status quo in our movement's membership standards cannot be sustained," he said.
Gates said no change in the policy would be made at the national meeting. But he raised the possibility of revising the policy at some point soon so that local Scout organizations could decide on their own whether to allow gays as adult volunteers and paid staff.
In 2013, after bitter internal debate, the BSA decided to allow openly gay youth as scouts, but not gay adults as leaders. The change took effect in January 2014.
Gates, who became the BSA's president in May 2014, said at the time that he personally would have favoured ending the ban on gay adults, but he opposed any further debate after the Scouts' policymaking body upheld the ban.
On Thursday, however, he said recent events "have confronted us with urgent challenges I did not foresee and which we cannot ignore."
He cited the recent defiant announcement by the BSA's New York City chapter in early April that it had hired the nation's first openly gay Eagle Scout as a summer camp leader. He also cited broader developments related to gay rights.
"I remind you of the recent debates we have seen in places like Indiana and Arkansas over discrimination based on sexual orientation, not to mention the impending U.S. Supreme Court decision this summer on gay marriage," he said. "We must deal with the world as it is, not as we might wish it to be."
Gates said the BSA technically had the power to revoke the charters of councils that defied the ban on gay adults, but said this would be harmful to boys in those regions
He also noted that many states have passed laws prohibiting employment discrimination based on sexual orientation, raising the possibility of extensive legal battles.
"Thus, between internal challenges and potential legal conflicts, the BSA finds itself in an unsustainable position, a position that makes us vulnerable to the possibility the courts simply will order us at some point to change our membership policy," Gates said.
He expressed concern that an eventual court order might also strike down the BSA's policy of banning atheists.
"Waiting for the courts is a gamble with huge stakes," he said. "Alternatively, we can move at some future date — but sooner rather than later — to seize control of our own future, set our own course and change our policy in order to allow charter partners — unit sponsoring organizations — to determine the standards for their Scout leaders."
Such an approach, he said, would allow churches, which sponsor about 70 per cent of Scout units, to establish leadership standards consistent with their faith.
"I truly fear that any other alternative will be the end of us as a national movement," he said.
The Utah-based Mormon church is the nation's largest sponsor of Boy Scout units, and in the past has supported the ban on participation by openly gay adults.
In a brief statement Thursday, the church said it would examine any policy changes "very carefully to assess how they might impact our own century-long association with the BSA."
Zach Wahls of Scouts for Equality, a group that has campaigned against the ban, welcomed Gates' remarks.
"Dr. Gates has built his reputation on straight talk and tough decisions," said Wahls. "It seems like the Boy Scouts will continue an internal dialogue about the subject and that a change within the next year or two is imminent."
The Human Rights Campaign, the largest U.S. gay-rights group, called Gates' speech "a step in the right direction."
"But, as we have said many times previously, half measures are unacceptable, especially at one of America's most storied institutions," said the campaign's president, Chad Griffin. "It's time for BSA leaders to show true leadership and embrace a full national policy of inclusion."
Until Thursday, there had been no indication how the BSA would respond to the New York Councils, which on April 2 announced the hiring of Pascal Tessier, an 18-year-old Eagle Scout. Tessier, currently finishing his freshman year of college, has been a vocal advocate of opening the 105-year-old organization to gay scouts and leaders.
Tessier had been getting legal advice from prominent lawyer David Boies, whose recent causes include arguing for recognition of same-sex marriage. Boies said it was possible that Tessier's hiring could lead to litigation between the New York chapter and the BSA's national headquarters, but he expressed hope this could be avoided.
After Tessier's hire, New York Attorney General Eric Schneiderman's office opened an inquiry into the BSA's membership policies and influence over local councils' hiring decisions. The office, which cited state laws against hiring discrimination based on sexual orientation, was reviewing Gates' remarks Thursday.
One of Tessier's lawyers, Josh Schiller, expressed hope that the BSA's ban would be lifted.
"People will join the Boy Scouts and look at them as an organization that has the principles of equality," he said.
Debate over the BSA policy has coincided with a steady drop in the organization's youth membership, which fell 7.4 per cent last year to about 2.4 million.
After the 2013 decision to admit gay youth, some conservatives split from the BSA to form a new group, Trail Life USA, which has created its own ranks, badges and uniforms. The group claims a membership of 23,000 youths and adults.
Trail Life's chairman, John Stemberger, said his organization was "saddened" by Gates' speech.
"It is tragic that the BSA is willing to risk the safety and security of its boys because of peer pressure from activists groups," he said. "Trail Life USA remains committed to timeless Christian values."
Associated Press writer Michelle Price in Salt Lake City contributed to this report.
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