WASHINGTON — Michelle Obama, after nearly five years of evangelizing exercise and good eating habits, will begin a new initiative on Tuesday that seeks to increase the number of low-income students who pursue a college degree. The goals of the program reflect the first lady’s own life and will immerse her more directly in her husband’s policies.

“I’m here today because I want you to know that my story can be your story,” Mrs. Obama is to tell students at Bell Multicultural High School in Washington on Tuesday, according to an advance text of her remarks. “The details might be a little different, but so many of the challenges and triumphs will be just the same.”

The first lady will add that whether students want to be doctors, teachers, mechanics or software designers, “you have got to do whatever it takes to continue your education after high school — whether that’s going to a community college, or getting a technical certificate, or completing a training opportunity, or heading off to a four-year college.”

Aides in Mrs. Obama’s office said she would visit other schools around the country and use social media to appeal to students, conveying the message that higher education is a door to a wider world. Mrs. Obama, the daughter of a pump worker at the City of Chicago Waterworks, graduated from Princeton University and Harvard Law School.

Many of Mrs. Obama’s supporters have been eager to see her use her résumé — before coming to Washington, she was an associate at the Sidley Austin law firm and a health care executive in Chicago — and her role as the first black first lady to expand her agenda. While she has also worked to help military families, her best-known initiative promotes healthy eating.

Some of her most widely publicized appearances — dancing at middle schools, doing push-ups on daytime television and promoting the arts ina video message at the Oscars — have made her popular and accessible. But she has also been derided by critics who hoped she would use her historic position to move more deeply into policy.

Others argue that Mrs. Obama has had to move cautiously and avoid taking on causes that might be seen as controversial or as beneficial only to certain segments of the population.

“She just could not have done this four years ago,” said Catherine Allgor, a professor of history at the University of California, Riverside, who has written books about first ladies. “If she came out of the gate with something much more tied to policy, she would have been shot down. Just look at the reaction to her suggestions that people eat salad.”

Dr. Allgor was referring to critics who say that Mrs. Obama’s push for people to eat better amounts to hectoring from a nanny state.

In her new project, Mrs. Obama will work with the Education Department to help further President Obama’s initiative to vault the United States from 12th to first in the world in the percentage of college graduates by 2020.

“When the year 2020 rolls around, nearly two-thirds of all jobs in this country are going to require some form of training beyond high school,” Mrs. Obama is to say in her speech on Tuesday. “You all are going to need some form of higher education in order to build a good career for yourselves and be able to provide for your family.”

According to the National Center for Education Statistics, 52 percent of 2011 high school graduates from low-income families enrolled in college immediately after high school, a figure 30 percentage points lower than the rate for students from high-income families.

Mrs. Obama had hinted in recent months that she wanted to expand her youth-focused agenda into education. “As we looked at the second term and what she was interested in, it was clear speaking to young people is so important to her,” said Tina Tchen, Mrs. Obama’s chief of staff.

Low-income students apply to, attend and finish college at far lower rates than their higher-income counterparts. Current research shows that even among low-income students with high test scores and grades,few apply to the most selective American colleges.

“I think this will have tremendous dividends around the country,” said Arne Duncan, the secretary of education. “She has a personal passion and authority on this because this is her story. This is her life. This is who she is.”

Mrs. Obama grew up on the South Side of Chicago but attended an academic magnet high school across town. In the past year in Chicago, she has led an exercise session with hundreds of city children and addressed 60 teenagers at the Urban Alliance, a group that offers professional job training and internships for underserved youth.

In each case, she emphasized that she and her brother, who also graduated from Princeton, came from the same place as the children and teenagers she was speaking to, and that college was the key to their success. One teenage girl who had been reluctant to apply to college came to the Urban Alliance after Mrs. Obama had spoken to her, recalled Sandra Abrevaya, the executive director of the organization. The young woman is now at the end of her first semester at Harry S. Truman College in Chicago.

Although the education initiative will bring Mrs. Obama a step closer to the West Wing, her staff said she would be more focused on young people than on policy, underscoring the practical limits of her power.

“The job of the first lady is both smaller and larger than the usual kind of career,” said Dr. Allgor, the University of California professor. “You don’t have a position or a paycheck. Yet we have this ironic development that we live in a time when women who occupy this office are more knowledgeable than ever about policy, yet we demand that they pull themselves away from that.”