Visions of what Rev. Martin Luther King Jr. would do to promote civil rights in 2014, had he not been slain decades ago, marked speeches and commemorations held across the country to honor his memory on Monday.

Recalling King's famous "I Have a Dream," speech, Atlanta Mayor Kasim Reed said the late civil rights leader would want school children to hear it as a call to stay in school and become educated to better the world.

"We need to swap the lesson plan for a dream plan," Reed told a crowd at Ebenezer Baptist Church gathered for the Martin Luther King Jr. Day federal holiday.

He said King would want children to hear: "You are not going to school just to study math, you're going to school to be somebody."

In New York City, newly elected Mayor Bill de Blasio, who swept into office promising broader opportunities for poorer residents, said at a tribute: "Dr. King would tell us we can't wait" to bring income equality to New Yorkers.

De Blasio vowed his administration would immediately "start the work of changing this city."

At the packed Atlanta church near the Martin Luther King Center, which promotes his philosophy of non-violence, King's daughter Bernice was applauded for her call to honor his message by making Monday a "no shots fired" day in the wake of school shootings and other gun violence across the nation.

One commemorative event was a buyback program organized by the Atlanta branch of the National Association for the Advancement of Colored People (NAACP) in the hopes of getting 1,000 weapons off the city's streets.

King, who 50 years ago received the Nobel Peace Prize, was assassinated in Memphis, Tennessee in 1968. He was born on Jan. 15, 1929, and the holiday commemorating his birth was enacted in the mid 1980s.

President Barack Obama and his family were among the many Americans who marked the federal holiday by volunteering for service projects and other charity events. They were part of the team at DC Central Kitchen, a local soup kitchen that was filling burritos with beef so the meals could be served to needy people.

"Sasha's technique is outstanding, by the way," Obama joked about his 12-year-old daughter as they worked together on the volunteer line.

For the first time, the National Civil Rights Museum in Memphis, which includes the Lorraine Motel where King was killed, publicly played a recording of a 1960 interview with him discussing the civil rights movement.

Magician David Copperfield donated the tape to the museum in 2012.

(Reporting by Barbara Goldberg and Ellen Wulfhorst in New York, Jon Herskovitz in Austin, Texas; editing by Ellen Wulfhorst, Chizu Nomiyama and Bernard Orr)