WASHINGTON — With the support of a string of 2020 Democratic presidential candidates, the idea of reparations for African-Americans is gaining traction among Democrats on Capitol Hill, where Speaker Nancy Pelosi backs the establishment of a commission that would develop proposals and a “national apology” to repair the lingering effects of slavery.

Nearly 60 House Democrats, including Representative Jerrold Nadler, the powerful chairman of the House Judiciary Committee, support legislation to create the commission, which has been stalled in the House for 30 years. The bill will be the subject of a hearing on Wednesday — the first congressional hearing on reparations in more than a decade, and the first on the measure itself.

“Reparations is a challenging issue,” Ms. Pelosi said in February at Howard University, adding that she supports the bill and looks “forward to an open mind and full participation of the public in that discussion.”

It is rare for Ms. Pelosi to weigh in on legislation before it works its way through the committee process, and in doing so she is entering an arena that is politically fraught for her party.