WASHINGTON — Mothers often have been important figures to American presidents, but rarely have campaigns highlighted their stories as prominently as with the mothers of Sens. John McCain and Barack Obama.

The Republican McCain often introduces or refers to his 96-year-old mother, Roberta, on the campaign trail. The Democrat Obama's late mother, Ann, a white woman born in Kansas, is central in his messages on racial reconciliation, health care reform, and the struggles of single parenting.

As the two presumptive nominees accept their party's nominations in the coming weeks, expect Obama and McCain to prominently share the stories of their mothers' struggles and triumphs. That they are such important parts of their sons' campaign narratives speaks to both the times and the particular traits of the two candidates. The mothers counter perceived weaknesses and buttress claimed strengths.

Roberta McCain is a living answer to questions about McCain's age; he'll be 72 on Aug. 29, and his father — a decorated Navy admiral — died of a heart attack at 70. Although Sen. McCain's campaign would not make her available for an interview, Roberta McCain has also been a personification of her son's maverick streak and straight-talk reputation.

The Arizona senator likes to tell about Roberta McCain's lead foot and recounts the time a few years ago when she went on a tour of France and was told she was too old to rent a car, so she bought one. When Roberta McCain told C-Span in the middle of the primaries that some Republicans might have to "hold their nose" to vote for her son, it reflected her son's appeal to independents and problems with Republicans more than legions of cable TV pundits have been able to do.

Obama's late mother, Ann, is a more complicated figure in the narrative of Obama's candidacy.

She died of cancer in 1995 at age 52. Central to Obama's biracial appeal is that Ann Dunham was white and from Kansas, and his father was black and from Kenya. Obama's "Audacity of Hope" — the title of his autobiography and a theme of his campaign — hinges on his own DNA, that if someone with his diverse background can rise to the cusp of the presidency, America remains the land of opportunity, despite its flaws. Campaigning in Kansas in late January before that state's caucus, Obama said his family spanned "miles and generations, races and realities."

Both parents are central to Obama's racial reconciliation narrative, one he often highlights in speeches. But the Illinois senator travels further with the memory of his mother, recounting her struggles with cancer when he discusses the need for expanding health care coverage and the challenges of raising a family as a single mom.

Obama's mother was a well-traveled, exploring woman, most remembered for her optimism and eclectic circle of friends on her way to a doctorate degree. She moved back and forth between Hawaii and Indonesia, where she studied women in native industries.

"She could be with and engage with and enjoy being with village women trying to make a living, or professionals in all walks of life," said Nancy Lee Peluso, a professor and environmental sociologist at the University of California-Berkeley, who met Obama's mother in Indonesia in the mid-1970s.

"She was very serious, very educated, very funny, very compassionate — self-made in a lot of ways," Peluso said.

Obama has written extensively about his mother's influence after his father left when he was a very young boy. He has said one reason he and his wife, Michelle, put down roots in Chicago was he moved around so much as a child, including time with grandparents in Hawaii, where he attended Punahou School.

Mothers of previous presidents have played prominent roles, some taking advantage of political or social trends.

"Miss Lillian" Carter, mother of Jimmy Carter, was outspoken at a time when debate over the women's equality movement was prominent in national politics. Richard Nixon devoted a big chunk of his resignation speech to his late "saint" of a mother.

Kathleen Hall Jamieson, director of the Annenberg Public Policy Center at the University of Pennsylvania, said in 1960 Nixon talked a lot about his mother, and John F. Kennedy's mother held campaign teas.

"But there is a more persuasive use (of mothers) this year," Jamieson said. "In McCain's case, it constitutes a rebuttal strategy. If you have concerns about someone's age, what is the most telegraphic way of dismissing them? (Roberta McCain) is not only coherent, she is quick and witty.

"On Obama's side, it anchors his narrative that he was raised by a single mother," Jamieson said.

She said Obama tries to lead audiences to a personally powerful inference.

"He says, 'White mother from Kansas, black father from Kenya.' " Jamieson said. "He is not making a claim about race, you are drawing the inference, because now it is more deeply lodged. Anytime the audience completes the message, it is a deeper message."

Peluso, the Berkeley professor, said she believes one reason mothers are getting more prominent attention is that "the role of women in America is finally being perceived differently," perhaps in part because of Hillary Rodham Clinton's presidential campaign. That's why the single-mother narrative is so significant, she said.

"The American family is changing a lot," she said. "And most women in America work."