WASHINGTON — First lady Michelle Obama is answering Republicans in Congress who want to roll back healthier school meal standards, holding an event at the White House to highlight the success of the health guidelines.

The Tuesday event is an unusual move for the first lady, who has largely stayed away from policy fights since she lobbied for congressional passage of a child nutrition law in 2010.

Sam Kass, director of Mrs. Obama’s Let’s Move initiative to combat childhood obesity, said a Republican bill that would allow schools to opt out of the standards is “a real assault” on administration efforts to make foods healthier for kids.

Kass, who is a White House chef, said the event is an attempt to point out the successes of some schools that have implemented the standards, which were set by the Obama administration and Congress over the past several years. School nutrition officials from across the country will speak about how well the standards are working in their schools.

“She wants to have a conversation about what is really happening out in the country,” as opposed to Washington, Kass said. “These standards are working.”