GRAPEVINE, Tex. — The Boy Scouts of America on Thursday ended its longstanding policy of forbidding openly gay youths to participate in its activities, a step its chief executive called “compassionate, caring and kind.”

The decision, which came after years of resistance and wrenching internal debate, was widely seen as a milestone for the Boy Scouts, a symbol of traditional America. More than 1,400 volunteer leaders from across the country voted, with more than 60 percent approving a measure that said no youth may be denied membership “on the basis of sexual orientation or preference alone.”

The top national leaders of the Boy Scouts, who pledge fealty to God and country, had urged the change in the face of vehement opposition from conservative parents and volunteers, some of whom said they would quit the organization. But the vote put the Scouts more in line with the swift rise in public acceptance of homosexuality, especially among younger parents who are essential to the future of an institution that has been losing members for decades.

The policy change, effective January 2014, is unlikely to bring peace to the Boy Scouts as they struggle to keep a foothold in a swirling cultural landscape, with renewed lobbying and debate already starting Thursday evening.