In the most comprehensive policy speech of her presidential campaign, Hillary Rodham Clinton on Monday presented her vision of a “growth and fairness economy,” an economic agenda intended to lift middle-class wages, expand social services, and increase taxes on the wealthiest Americans to combat a widening gap between rich and poor.

Mrs. Clinton said “the defining economic challenge of our time” is raising incomes for the vast majority of Americans whose wages have remained virtually stagnant for 15 years as the costs of housing, college, child care and health care have soared.

“We must raise incomes for hard-working Americans so they can afford a middle-class life,” Mrs. Clinton said in a speech at the liberal New School in Greenwich Village in New York. “That will be my mission from the first day I’m president to the last.”

The widespread feeling that the economic recovery has not benefited large parts of the population has helped frame the 2016 presidential race. But devising an agenda that addresses income inequality without vilifying the wealthy has been a central challenge of Mrs. Clinton’s early candidacy, and for weeks she pored over policy briefings and academic papers and fielded advice from 200 policy experts who often offered divergent opinions.