Jimmy Carter and Walter Mondale have surpassed John Adams and Thomas Jefferson as the U.S. president and vice president who have lived the longest since leaving office.

As of Tuesday, Carter and Mondale had lived 25 years and 123 days since leaving the White House in 1981. That's a day longer than Adams and Jefferson, who both died July 4, 1826, exactly 50 years after the Declaration of Independence was signed.

More important than their longevity, some observers contend, is the legacy of productivity the pair have crafted.

"The modern presidents seem to be living longer," said Jay Hakes, director of the Jimmy Carter Library and Museum in Atlanta. "The question of what they're going to do when they leave office assumes a lot more importance now than it may have in the past, and (Carter and Mondale) have really sort of set the pace for very active and productive lives after leaving the White House."

Carter, 81, and his wife, Rosalynn, founded The Carter Center in 1982. He has traveled widely since then, working on peace, democracy and health initiatives worldwide. He won the Nobel Prize for his efforts in 2002.

Carter's other pursuits have included volunteering annually with Georgia-based Habitat for Humanity, which builds homes for the poor, writing more than 20 books, and hobbies that include painting and woodworking.

Four years after leaving the White House, Mondale, 78, was the Democratic nominee for president. He was appointed ambassador to Japan by President Bill Clinton in 1993 and was Clinton's special envoy on the Asian financial crisis and economic reforms in Indonesia five years later.

After Sen. Paul Wellstone of Minnesota died in a plane crash during his re-election campaign in 2002, Mondale replaced him on the ticket but lost to Republican Norm Coleman.

Mondale currently is senior counsel at Dorsey & Whitney LLP, a Minneapolis law firm, where he specializes in issues involving Asian finance and government.

"He comes into the office nearly every day," said Larry Splett, a spokesman for the firm. "He remains very active and engaged."

Mondale was traveling overseas and could not be reached Tuesday, Splett said.

Carter, meanwhile, was hosting a Carter Center forum of human rights workers worldwide. In opening remarks Tuesday at the Human Rights Defenders Policy Forum, Carter did not mention the milestone.

In a 2004 interview with The Associated Press, he said he decided early on to use the clout from his presidency in the years that followed.

"I have been blessed by graduating from the White House at an early age," he said. "Enough so that I could use the prestige and fame and experience from being president of the greatest nation in the world to have access to leaders and understand the problems that they face."

Carter was 52 and Mondale was 48 when they took office in 1976. Carter was defeated by Republican Ronald Reagan in 1980.